My entire collection was bought through ebay UK.
The trilogy you "lost" I got for under two quid plus postage and most of the rest were between 50p and three quid plus postage. I paid a bit more for the early releases but they are much rarer. The Executor box set was only 99p plus postage but that was a very bizzarre fluke.
I am glad you liked the VHS page from my site so if you want to see more and look at what LD transfers, edits, projects etc are out there on DVD, go here.
Ell referred to trades that he was willing to do and I suspect that many of the titles he has will be listed here.