Actually the reason they cost that much, is because they are POPULAR old analog synthesizers... the Moogs, The Arps, The bigger Rolands (Jupiter 8, TB-303 etc)... it's simply some kind of "prestige" kind of phenomenon.
You can get lots of old analog gear out there, that has somehow went into "The book of forgotten synths", that will do a very well produced analog sound... funnily enough, most of the most expensive vintage gear, is the most quirky and undstable of them all atually.
There are many analog or analog hybrid synths from the 80's and 90's that are much more stable than the older ones, have much more power and features, but still sound VERY analog! And that can be had these days for almost nothing...
And many current synth manufacturers also make analog synths these days, that are one hell of a lot more stable than the old ones... like Vermona, Dave Smith Instruments, MFB etc... surely some of these are pricey, but they do generaly not cost that much more than their digital competition, and in my opinion sound much better (a mater of taste of course).
Usually, if you want analog at a low price, you'll have to look for the monophonic ones... MFB make very cheap analog synths and drummachines. Dave Smith Instrumetns Evolver, and Mopho are superb, and sound stunning.
If you want Polyphonic Analog synths you have to be willing to spend a bit more though... but Vermona, Dave Smith Instruments, Jomox and many other makes these, and sound as good as the old vintage ones.
If you want dead cheap analog polysynths you can look for some nice machiones from the 80's like:
Oberheim Matrix 1000
Roland MKS-50
Waldorf Microwave 1
Ensoniq ESQ-1
Ensoniq Mirage
Korg Poly-800
Korg EX-8000
Roland Junos, JX8P etc.
there are probably more, you just have to forget about the Vintage Syndrome and believe that those are the only machines that will "do the sound!"... shure, if you want autheticity you have to get the real thing (we all know that from SID 6581 right?

).
And by the way: solder a MIDIBox 6582 will give you a nice 8voice SID polysynth as well, and if you can do the soldering yourself, it's cheap!
