Obviously, the longer the track, the better the flotation in deep powder. The trade off to the super long tracks (162+) is in being able to turn them. Going through the trees becomes an aerobic exercise for some guys on a really long track sled. It used to be that 136" was long, then 144", then 151". Now the 155" is considered a moderate length.
There are a ton of sleds out there that will fit in your budget. Polaris, Arctic Cat, and Skidoo all made very capable sleds in the recent past that will work. My favorite would be an RMK (avoid the 05-06 900 and the 06 700, that engine was only produced for those two year.) A close second would be an Arctic Cat M7. I tried the Ski-doo rider forward position and it just didn't fit me very well, but I know guys that love 'em. I'm not much of a Yamaha 4-stroke fan, in the deep powder, they are pretty nose heavy.
Good luck in your search!