It takes patience on eBay. I was able to get a Revolver Ocelot and Solid Snake from the MGS1 line for $18 and $17, respectively, and that was only like 2 weeks ago.
ive got revolver ocelot and pyscho mantis from mgs1 and i have the whole set of mgs2. i was a dumbass when i was younger though and took them all out of the boxes and threw the boxes away