It really depends what you would be using the computer for (gaming, everyday use, music, etc.) but the best deal I can find for everyday use computers is at Wal-Mart stores.
Nothing!!!!!!!!!
Any kind of touch screen keyboard can be used with a desktop computer. The only requirement for a touchscreen keyboard is a touchscreen monitor. One of these monitors can be purchased for anywhere from $250 up to $700.
You can find a Garmin GPS system for under $250. There are many people selling used GPS systems for under $250.
You its a EPIC fail in desktop defender you will needs to send a comment to casual collective good luck 
By the fuse box under the steering wheel
passanger side firewall under hood
+- 250 watt to 500 watt
There are many desktop photocopiers that can be purchased for less than $250. The Canon PC170 Portable Desktop Copier comes in around $150 for a new machine. It is also portable.
Not known ,but there are case tower fans for the computers
You won't get a good e-guitar for less than £250. I think you should set your budget at at least £250 and maybe aim for an epiphone, takamine etc.
Check The Boltons Hotel. Online travel sites will usually have rooms under $250 and the hotel gets good reviews. The hotel's link is below.
You can find video cameras under 250$ in any of the main electronic stores like Best Buy. You can also check Amazon's website to compare prices and get the best deal.