All original and unmolested?
It's tricky because these are ALWAYS "modded". Try finding a decent original 6309 diver that hasn't had a nasty garish bezel fitted, or been turned into a cheap looking "ScubaPro 450" knock off. eBay is flooded with them.
The midsize diver is a cheap one, maybe £50-£70. The two big 6309 models I'm guessing should land anywhere between £100 and £200 depending on the condition of them.
**Edit** Quick flick through eBay shows some of the midsize models clearing £100. Depends on the variant. A quick group pic of them would help a lot.