If it helps, I have had two experiences buying Mac RAM on eBay.
Recently I bought a 512MB PC133 DIMM for my Digital Audio G4.
It was advertised as Crucial brand, CL2, and pulled from a Quicksilver.
It was $25 with free shipping and works fine. The seller's username was "videopuppy".
A couple of years ago I took a chance on cheap RAM on eBay from a different seller (advertised as PC only) and it didn't work at all.