Inexpensive? I haven't found one yet.....
Any of the grinder manufacturers such as Bader, Wilton, Hard-Core make contact wheels. The Bader and Hard-Core wheels are not as expensive as Burr-King, which still has these parts available. As far as an idler, Texas Knifemaker's Supply has a rubber coated idler that is reasonably priced.
A friend of mine made a grinder that has a 10 inch Burr-King contact wheel with the idler from Texas Knifemakers. It is only a two wheel grinder as opposed to three wheel, ala Bader. It is very smooth and he adjust tracking on the idler assembly. This maching works very well and he spent less than $500 on it. This is not bad at all considering what I just spent on a Hard-Core.
C Wilkins