First and foremost you need to make sure it doesnt have the dreaded third hole. Google 3rd hole mak-90 and see what I mean.
Next is current market values. I wouldnt pay more than $800 for one new in box. $650 for a used
The straight cut receivers are the one to buy as the slant cut are nearly impossible to find a stock to fit.
Also the milled are more desired if you can find one they are typically a bit more costly at $850-$1k.
If you can get real lucky and find a National Match under $1k you have the best Mak ever produced. But I wouldnt pay anymore than $1100 for one. Goodluck bro