well... when my friends and i tried pulling this stunt a few years ago he started with an old Korg, similar to the poly 800 but with a cool twiddle stick on the left side.
they're generally still pretty cheap, ESPECIALLY compared to Moogs - although if you really want that old Stereolab sound it's what you want. their 'horns' were all from the Moog Concertmate, apparently it sounds like garbage for anything but emulating brass but it's the best brass emulation in a synth.
one thing to be ABSOLUTELY CERTAIN TO DO FIRST when dealing with vintage analog synths is TRY IT BEFORE PAYING! this cannot be stressed enough, ESPECIALLY with an analog synth. the sounds from one class will vary from model to model as the years would have taken their toll on the internal components. it CAN result in wonderfully unique sounds that would never happen anywhere else, it can also just as easily result in atonal buzzing regardless of what key is pressed - which is great if that's what you're looking for.
i'd say an early 80s Korg is a good starting point. also, this site will be your new friend -
Vintage Synth Explorer