I'm about your size, and I've been recovering from a fairly serious back injury, so I've become rather picky about chairs. I have two favorites, but neither one is what most people now days would think of as a "desk chair". I like a solid chair that doesn't move around, no wheels, no tilt, just a place to sit.
If your willing to do a little thrift shopping you can get a [Wooden library chair][1] for about $20, or you can buy one new for about $150.
$150. If you want a similar feel, but don't care as much about the appearance, a [Lifetime plastic folding chair][2] will sit about the same.
It's surprising how comfortable an old fashioned chair is. You won't get that immediate "wow" feeling when you first sit down, but I find myself using better posture and varying my sitting position more frequently than with a typical modern desk chair. Also, with no moving parts, they really do last forever.
[1]: http://www.uslibraryfurniture.com/study-seat-5/classic-library-chair-ja303b-m.html
[2]: http://www.amazon.com/gp/product/B0002QZ2G4/ref=pd_lpo_k2_dp_sr_2?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B00085FN7C&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0Y3XR4WCRDK0MH4QF9F5
