I think you should try to buy a fully built A1200 tower from eBay as this would be the cheapest route to getting a capable classic Amiga, this will cost around £300 and would get you a good system.
You should be aiming for something like an A1200, 1260 accelerator, 64mb ram, Mediator PCI board, voodoo(3/4/5), network card and maybe a soundcard, CD Drive, FAST ATA, scandoubler(if your lucky).
There are other routes to go, you could build a tower from scratch which although far more expensive lets you pick exactly what you want and if you buy the components from a dealer will come with some form of warranty even if the parts are second hand. If you do this you'll need to ask yourself if buying an A4000 is a better option.
