W5 Heads for sale.. how much are they worth?

All depends on the buyer and plans. Unported, un modified units are getting harder to find, and if they were never run and unmodified that would make me wary. W5s had some serious issues with porosity and quality control that are well known. If I was buying and didn't know you from Adam - I'd lowball expecting to have to have everything closely inspected by someone who's got experience with them. If you have shop reciepts, flow testing records, or any paperwork to back you up that would help. To answer you - they're worth what someone will pay.