Answer: As a rule of thumb, do not expect anything within rye Garden Ring to have "affordable prices". I think Atrium (at the Kurskij railway station) and Olympic Plaza (at Prospekt Mira) is about the closest you can get to the city center without paying a significant premium "for the prestigious location".
Aside from that, there's not too much variety in price ranges of various shopping malls and trade centers located between the Garden Ring and the MKAD. Make you choice basing on your location and convenience: for example, if you are staying somewhere around the Third Ring Road, venturing to one of the out-of-city malls, such as MEGA, would be less than ideal.
Be advised, though, that shopping malls in Russia are a very "middle class, and above" way of buying things. Those wishing to save heavily (such as the retired seniors) would seek other places and options to buy both consumables and long-term use goods.