Too much...? http://www.hitc.com/en-gb/2017/07/10/blackpool-set-asking-price-for-barnsley-target-brad-potts/
Dulwich Hamlet seem to think the fee was around £500k according to this: https://www.londonnewsonline.co.uk/26867/dulwich-hamlet-set-bank-50000-defenders-switch-barnsley/