I have just read an article about the Kew Gardens 50p coin. Apparently they are selling on ebay for up to £120 !
Im a little gutted about this as I remember digging up a 50p coin on filey beach last spring which had that design on. Unfortunately any of the larger coin change I find ends up in a tesco self service machine so there is no chance of me getting £120 for the one I found, Doh!!
So check your 50p's before you make the same mistake as me.
Here is a link to the article