I guess you have to ask how old it is, but I would start the bidding at around £200 and maybe settle for 250-275. Incidentally I think your sign off quote "Kings and Queens etc " is afflicted with some floating possessive apostrophes!
I bought an AX3 that had spent 5 years unused in a locker for £250, the problem I had after about a year the glue that holds the transom on failed. I did repair it with two part glue.