You certainly don't need to spend 100 pounds on a prototype PCB!

There are many companies that will do you a good prototype at a sensible price - I particularly like the ones that do a fixed price based solely on the size of the board, no mesing with number of holes and how many different sizes of hole, etc.

I've had good experience with both prototypes and small production quantities from PCB-Pool
http://www.pcb-pool.com/html_uk/uk_angebot_2.htm.

The quality is good and delivery has always been exactly as stated or sometimes even sooner.

And helpfully they take native format board files from many different PCB CAD programmes so you don't even need to convert to Gerber.

And best of all, if your boards are smaller than the 1dm2 minimum board area they will panelise them for you and charge for a single minimum size board. This is great if you're having really small boards made and will save you a fortune.

I have looked at some of the US based services but in most cases the delivery charge makes the total cost rather high. (I'm in the UK like you).

Other people have recommended Olimex and they have been supplying to e.g. members of the PICList for quite a while now - and piclisters are quick to discover and point out any problems so they may be worth trying too.

Hope this helps.