I went to a BCA auction before christmas, I was looking at cars for about 1k, the fees added would have been about £200, iirc it didnt go up that much for the budget you have, naybe £300.
I didnt find anything, but had an interesting morning
There are additional 'fees' for paying by cash (1.5%) credit cards (3%) and a £10 fee to send off the log book. (These percentages are iirc but not miles out).