They don't cost that much, and it also depends on where you are. I suggest you approach your electrician or electrical supplier, explain to him what you need it for and then he will then tell you the cost. Installation will be extra, as you can guess.
If your spa is connected with a GFCI circuit breaker you will not need the GFCI receptacle.
GFI is a mini circuit breaker that responds to shorts or contact with water
If the GFI outlet is tripped (the outlet, not the breaker) then it is telling you there is a ground fault which must be fixed. If the GFI outlet is not tripped, and the breaker is not tripped, but it is still not providing power, then you have a loose connection or a wiring error.
If you're using a GFCI breaker then the entire circuit will be protected by just the breaker alone. Every receptacle, switch, etc on that breaker will utilise the GFCI protection. You may have problems with it tripping if you plug in a motor (vacuum, etc) on the circuit.
If the GFI that is tripping is a different circuit, there is electrical leakage between the circuit the GFI is controlling, and the dryer circuit. It is possible that there is some cross wiring in the electrical box. I would strongly recommend getting a licensed electrician to look at it, preferably before you have a fire. If the GFI is the same circuit as the one where the dryer is plugged in, you might want to have the dryer checked for leakage to ground. You should also check the dryer circuit's rating against the rating of the breaker in its circuit. A dryer typically takes 30A on usually a single two-gang breaker; if you have a larger dryer that pulls, say, 45A, a 30A breaker will always pop. It sounds to me like a bad electrician has, instead of buying a proper two-gang 30-A breaker, installed your dryer across two circuits, one being the garage GFI circuit; the dryer, because it pulls 220V, pulls an unbalanced load across the GFI and triggers it, and the other circuit breaker is triggered because it loses the extra power provided through the GFI. I cannot emphasize this enough: get this checked out and fixed. Now. Before you get a house fire.
GFI (or GFCI) is an acronym for Ground Fault (Circuit) Interruptor. Essentially, it is a current sensor. A GFI outlet or breaker monitors the current flowing through both the hot and neutral wires. If there is a difference between them, that means electricity is leaving the normal circuit and is flowing through something else (probably you). The GFI watches for this difference and shuts off power to the circuit if an imbalance is detected. This is why a GFI is mandatory for pools, bathrooms, etc.. If you happen to become a conductor because you are wet, the GFI will detect the current flowing through you and shut the power off. A normal breaker will only shut off if your body happens to overload it, which is unlikely.
Check the circuit panel / breaker box. The tripped breaker should be partway between 'OFF' and 'ON'. If nothing else, turn the breakers off then on, one at a time and when the tripped breaker is reset, the circuit should be live again. Also check GFI outlets. If one is in fault condition, it will need to be reset. If the tripped GFI outlet is protecting other outlets, they will come back when the tripped GFI is reset. These sockets seem to hide in many cases... Behind microwave ovens for example or refrigerators.
If t hat GFI is the only plug on the circuit then yes. If there are other plugs you have to find out how many so that you don't exceed the capacity of that circuit. If the GFI is the only plug there, turn the power off to it at it's breaker and run the appropriate wire to the new plug you want to install. Wire in the new plug, then make the connections at the old GFI plug. Always work towards the power, even if the circuit is dead. It's good practice. This way you rarely if ever have to work on live circuits. Start at the furthest point in the circuit away from the electrical panel and work toward it. You can have the new outlet protected by the GFI if you connect the wires from the new outlet to the LOAD side of the GFI. If the GFI is still new there is usually a yellow sticker covering the screws, those 2 screws are the LOAD side meaning that if anything happens downstream on that circuit to make a GFI trip the GFI will sense it and turn the circuit off. If you want just a standard outlet then put the new wires on the same screws as the old wires on the GFI. Once you're done, and all the boxes are closed and safe, turn the breaker back on.
If the outlet cover was held open by the lights it could be wet. A smal amount of water will cause a GFI to trip. A GFI is a device which makes certain that voltage is not draining away from the two wires, to some OTHER voltage drain, such as a human body or a wet circuit. if above not the answer go to your breaker box and find the breaker that controls that circuit. you will know when you have the right one when the breaker does nothing, not even trip it self. see what else is on that circuit {what else turns off when main breaker is tripped and unplug everything that is on that circuit then turn on the main breaker. try the reset with everything else off if it still trips then its the gfi itself. they go bad often on construction sites [my own personal experience] if it resets properly than one of the other things on that circuit is the culprit. replug or turn them on one at a time. the breaker will trip if its one of these. if not replace the breaker. pretty cheap at lowes or home depot. turn off main breaker when you replace it. lots of luck!!
Because of resistance drop; if the cable is too long, you could be drawing additional amperage because of line loss (inductive load), or losing excessive power in the cable. Additionally, the gauge of the cable should be considered as well. If you are using a GFI circuit breaker, too long of a run can cause the GFI to continually pop because of inductance and line loss.
A Class "A" Circuit breaker is a Ground Fault Interrupt (GFI or GFCI) breaker ."Class A" marking -- A "Class A" ground-fault device is intended to protect people. The Class A marking indicates that the trip threshold of the GFCI is between 4 mA and 6 mA. This marking may be in any location except the back.
The circuit that the GFI controls has a current leak on it. The leakage could be anywhere in the circuit.To trouble shoot the circuit first shut off the GFI breaker to the circuit in question. Then remove the load (pool light) from the circuit. Isolate the feeder wires with wire nuts on both the "hot" and neutral conductors.Turn the GFI breaker back on. If the GFI breaker does not trip when it is turned back on, the problem is not in the feeder wires. The tripping problem is caused by the light fixture. If the breaker does trip you will have to find where the moisture is getting into the underground conduit system.Remove the light fixture and try to completely dry the unit. This can be done with a heat gun by blowing hot air on the fixture to dry it out.Once you think the fixture is completely dry, without placing the fixture back in its placement in the pool, temporarily connect it to the feeder wires and check to see if the breaker trips. If it does not trip then you have corrected the problem.What is left to do now is to find out where the leak is that is letting the moisture into the fixture. Once found and completely sealed the fixture can be placed back into service.