Ok, getting closer and closer to an actual decision basically, I've narrowed it down to 2 options each having two sub-options: 1: a complete bike, which would be the Fuji Feather or the Maze (which depends on how I like the Maze when I see it), or 2: build one up, either based on an old road-bike frame with good parts or a good new frame with cheap parts.

I'm leaning towards just buying a complete bike, for a number of reasons. Basically, for the money I'm looking to spend, I don't think I'd be able to build something that's any better. Of course I could get some cheap parts to replace later on, but that'd still mean spending more money Plus, I'd rather have something overall decent than something half good/half bad to start with. The LBS I mailed responded that they can't build anything up to their standard for 650 euros, but that they can build (or help build) something based on an old frame.

Now, I know many people say this is the way to go when getting into fixed gear riding, but, I'm not convinced yet. First off, I'd need to buy a second hand frame, clean it, strip it and have it powder coated (assuming I don't want to keep the old and worn paint). While not as expensive as a good new frame, it would probably still set me back about 200 euros altogether which means I'd still not be able to build it up with anything exceptional (probably around the same quality parts a one of the complete bikes to be honest).

Plus, it's bound to have drawbacks as well... apart from having to find one in the right size, with proper geometry, horizontal(ish) dropouts and in decent state, how good will an old frame actually be? A lot of new cheap bikes get shot down here because they aren't CrMo, does this mean that when looking for an old frame I'd have to know exactly which frames are and aren't good?

So, it seems to me that in the end, building one based on an old frame would not result in a better bike... unless I happen to find a magnificent frame cheap and get lucky on the parts.

So I'm thinking I'll go for a complete, new, bike, unless someone can convince me that it's not the best option (I do think I'd enjoy building my own bike, but I don't really have the time for it so the initial building would be done at the shop. I will be doing most of the maintenance myself either way).

Thanks for all the replies so far... almost there!