Budget around $200 per scope and pick up both a compound and a dissection would be the best bet. You can pick up a decent stereo dissection in that range.
Heres my bench (dont mind the mess) The stereo is a Konus Opal 40x dissection that I picked up for about $120 new and next to it is a cheap hobby lobby 400x compound that came with a little usb camera. I use the compound for counting cells but really most the time it's the stereo dissection that pays the way!
Since most of my clients are engineering companies I often run across used stereo setups (they use them for soldering small parts and such) ranging from super low to super high end... IMHO
the Konus does it's job at a great price! A better compound is in the future for me but not till I finish acquiring the rest of my lab wish list as this one will do find for now. So far Ebay has been wonders, I've been able to pick up my microfuge, tubes, a micropipette (much valued peice of equipment) and a few water baths on a very tight budget!