Might be a great deal, but it is hard to tell from those photos. I wonder what the underside looks like. With all that rust starting to show it would make me move very carefully if I was looking to buy. Although it is a nice unmolested car.
Classics are tough because it is about stiking a balance between price, work done and work needing to be done. Throw in a smattering of "parts it has vs. parts I will need to get" and you can start to get how good a deal something is. As for the car posted, it has visable rust in most of the usual spots with the rot on the front wing looking "advanced." Sounds like the seller may have worked out some of the current mechanical bugs but keep in mind, even in the best shape, this is still just an 850 which most would consider under-powered (even by classic Mini standards.) It does have a cool gauge cluster. I don't think it is clearly a great deal. It may be a good deal but it also may well be a complete money pit. Just not enough there to tell.