OK, found one on Gumtree in Paulsgrove near Portsmouth, un-opened for £60, but the woman hasn't answered emails and phone calls, so I don't know if it's still available, but I'll keep trying.
Failing that ToysRus sell them for £99.99. I could stop off at the Woking branch, if they have them in stock, and buy one en-route. Would one more person be happy to contribute the additional tenner?
I now have work for both Tuesday and Wednesday, so it will have to be Monday that I take it up to Chugs field ... hope that's OK Chug? If there's no one there I'll have to hide it somewhere on site.