So I've built myself a motorized slider, and it works great. But I'm tired of lugging around ladders and other unsightly equipment to mount it. Its 36 inches, weighs probably about 25 lbs. I have a manfrotto quick release I can mount to the legs directly, probably cheaper and more ridged, though being on a head would be a lot nicer. I don't want to spend a lot of money, all this thing needs to do is hold it still, no fancy panning, dragging, etc. I figure I could find some used old school beat up but heavy duty tripod legs cheap, but I don't know model numbers and the like. I'd like to avoid spreaders.

Any suggestions for my ebay search?

I use this one with my DIY slider and jib. My slider is 28 inches and my camera is 5.4 lbs. I spread the legs wide and have never noticed any unwanted movement. I never raise the center column as this would affect stability. This tripod is rated for 30 lbs.
Amazon.com: Davis & Sanford ATP All Terrain Tripod without Head: Camera & Photo (http://www.amazon.com/Davis-Sanford-ATP-Terrain-without/dp/B001TUYUF6)

There we go, that is what I'm talking about. Thanks a lot for the recommendation!

For heavy duty, I used to love the 3036. Don't let the pics deceive you though, this tripod is heavy!
Bogen 3036 Manfrotto Professional Tripod | eBay (http://www.ebay.com/itm/Bogen-3036-Manfrotto-professional-tripod-/140999483922?pt=US_Tripods&hash=item20d4396212)

Not the most elegant solution, but in a pinch, you can use almost any tripod at one end, and a cheap monopod at the opposite end. It will be surprisingly stable.