That might be a freak Ebay price at one time. Most of the Grapevine's are worth 5 or 10 each. Trust me, I sell them week in week out. I just Ebayed a demo of Flame & King, it went for less than 20 quid, and thats supposed to be "£50". You may see Grapevines on lists for 25's and 30's but do they ever sell?
Simon, when you say they are in RCA demo sleeves, are you counting those as actual demos?
If all your 45's marked D are proper demos, I'll be willing to make you an offer, cash or/and trades, seeing as my complete set was stolen by someone I will be perfectly happy to name by PM.