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.
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.
Not known ,but there are case tower fans for the computers
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.