I bought mine direct from the Autosportlabs site in the USA
Currently about $89 + shipping for the basic DIY kit
Autosport labs USA
Some good info on this site too
You can buy ready assembled in the UK from triggerwheels, but it is likely to set you back about £175
The exchange rate is not too bad at the moment, Paypal will give you a decent rate..............Unlike my credit card issuer & my bank
Probably get a kit with all the bells & whistles (USA) for about the £100 mark