Bcb used to have one that was under $300, don't know if john still offers them or what the current price it. Just looked on his web site, which hasn't been updated in years and he list like $300+ plus calipers, but iirc when I was working on my own conversion he told be directly that it was cheaper than that, I guess you'll have to call him.
I don't know what Jeff has available, but I wouldn't hesitate to buy from him.
Iirc there was a guy on e-bay that had a fairly low priced set up.
Or its dyi. Dyi will probably be the cheapest, but require the most effort sourcing the parts yourself (for me it required a couple trips to various parts houses and a little experimenting, it definitely wasn't one-stop shopping, although it couple be close to that). Thats really what your paying anyone else. Part prices, markup (got to stay in buisness some way), shipping and a little profit for the effort of making it easy for you.