are you talking about an adjustable guide to butt your stock up to when cutting multiple pieces? If so, why are you wanting an electronic version? I've seen very good, very easy to use (read: fast) mechanical stops. Most of the time these are used on sheet metal shears, and have incremented guide rods that stick out, with knobs to quickly adjust the length and a locking mechanism to keep the stop in place once adjusted. I fail to see how an electronic version would be much faster, unless you are adjusting from 1"-20' or some huge range like that.
If you are dead-set on an electronic version, I would think that an acme screw driven by a servo motor should work fine. For cutting with a chopsaw, I doubt if you would even care about the backlash in your acme nut/screw assembly. Your desired input could be set with an N-turn pot., I'm not sure what controller you would use, but I'm sure they're available. Heck, an open loop system may even be accurate enough... I'm just rambling now. Let us know more of your needs, I'm almost sure we can find/make something cheaper than $800.