Yes, the C lenses are indeed the oldest and cheapest. Be careful with those: shutters cannot be repaired for lack of spare parts. If you get one, ensure that it is fully operational (or that you have a good return policy!)
Black C lenses have a T* multi-coating (same as later CF, CFi, CFE) while silver C lenses do not.
Difficult to name a price as it varies by age, condition and geography. Current ebay ask prices for a 80mm C are all over the place, some over 1000€. This is bonkers. For this price you can have a nice CF lens!
My personal limit - therefore take it for what it's worth and I hope I am not violating any forum rule here - is 300€ for a private sell and 500€ for a CLA'd lens sold by a store, with warranty. Any price higher than that represent too much risk in my opinion, I'd fork out the difference for a CF or later lens.
To me, CF represents the sweet spot of the Hasselblad lens lines, for several reasons. This topic has been debated extensively on this forum (you can search for older threads on this)