Well for the regulator itself on ebay they have em for $20 and up.
Search results for Interior Window Motors & Parts Nissan in Car & Truck Parts & Accessories
Or youd probly be better just to buy them together, Here is one also on ebay for about $44. Brand new with motor and regulator.
eBay Motors: WINDOW REGULATOR nissan MAXIMA 89-94 rear 90 91 92 LH (item 370041226291 end time Apr-16-08 15:50:40 PDT)
I got mine on ebay aswell and they are a good deal. Unless you wanna call around to local shops but then you will probly end up paying double the price
