www.4wheelparts.com has the following deals (you can use these prices as leverage at your local shop)...
15x8 black rock crawler rims w/
31x11.5 Supr Swamper LTBs $608
www.DesertRat.com has same wheel w/
31x10.5 Mickey Thomas FC2 or Radial Claw $540
31x10.5 Conti Mud-Trac on MT Classic2 or Desert Crawler wheels $720
With 31's you may need to crank your T-bars an inch or 2 but that should do the job.