Benchmarks are nice. They can be found for surprisngly little now. Most people don't want slide frames so they can be scooped up for pennies on the dollar. I purchased a (NIB) benchmark slide a week ago, off e-bay, for under $6. Kapp is selling trigger plates for $1 right now, and due to some lucky e-baying I scored an Equalizer Sear for $11.
So, it is possible to build a really nice slider for on'y about $20 with some luck. Check the e-bay for any of the frame metioned. That's my best advice.