I paid $200 for my CMVS, a two slot. This was with a UniBIOS an OG stick and a Neo CD pad. I invested another $70 or so converting it to component video (changed from JROK to NeoBitz).
When released MVS was more expensive since it was aimed at operators, $700+ per cart or whatever, while AES was...well, they started in the mid $200s but ended in the mid $400s. Now it has flipfloped completely with most MVS games being under $100 (many less than $20) and many AES games fetching $1000+.
Say what you want now, but you WILL want to play the newer games. Why the hell wouldn't you? For MVS I have Metal Slug 3, KOF 2003, Rage of Dragons, etc and the most I've ever paid for a cart was $90 and that was for Pulstar. The purchase price of the CMVS can easily pay for itself with the FIRST GAME you buy.
And since you will ask, yes, there are converters but they cost as much as a system so they are, IMHO, as pointless as possible.
Functionally and fiscally the CMVS beats the shit out of AES in every possible way. If you want "that feeling" or you just like staring at systems instead of playing them, then by all means get an AES. If you actually want to play the shit then AES is just painting yourself into a corner.