There are a lot of duff resonator guitars about, as well as good ones. The best in the world are made by a firm in Leeds (called, I think, Beltona - one loses interest at 4000 GBP). Music Ground in Doncaster usually have a couple in stock, and the Guitar Player in Rochdale is worth referring to. It sounds like you haven't played seriously for some time. Find someone to appraise the instrument before you commit yourself - the price sounds OK, but if you get seriously into bottleneck you'll probably want to finger some notes as well, and it is no good if you get that far and find the action is too high or the neck is twisted. If you're nervous, leave a deposit of not more than 20GBP to stop the shop from selling it - if you don't buy it, you'll lose the deposit, but you won't lose the chance to make your decision.