Tons have been written on this.
I shopped for a long time and found the best deal on a pressurized sand blaster was The Texas Blaster. 350.00 for the blaster at the time. They also carry a cabinet blaster. Next check your air supply. If you are not pushing 15-20 sfm, then you are not doing much. I rented an air compressor and blasted all two days and primed the next. 1000 pounds of sand.
It all gets pretty expensive, so... like the guy said earlier, if you aren't using it often, go have it done.
If I had it to do over again, I would have spent my money on a good cabinet blaster and had someone else do the frame and body.
