Alex,
Robinia burrs very easily in the UK. It is native to the South East of North America where it grows straighter and yields planks. It was planted extensively by the Victorians in their desire to create Ornamental gardens. The wood will shift little when you cut it but the flame and burrs will contract and move significantly. I'm afraid I don't concur with Frankie on the value, its certainly not worth £3 a blank to a purchaser, more like 50-75p and if thats the cost, to be honest its not worth acquiring if you reckon you are going to cut it and sell it on.
It difficult to price because nobody to my knowledge stocks robinia burrs, s its worth what you can do with it. £10 tops?