Have you considered using Invision Power Board (IPB)...? We used to swear by VB and UBB, but have migrated 95% of all our client sites to IPB over the last year.
Just a suggestion... (I don't work for them, hehe).
I just did a search on eBay and didn't see any Vbulletin licenses or sites for sale (nor recently on sale)...
One thing you may wish to do is check out the forums of competing forum products (phpbb, infopop, invision, snitz, gossamer forums, etc.) and see if any "expatriate" VB users are selling their licenses.
Cheers,
Rob