I also use £80-100 as benchmark to bid through easylive. if i guess my winning lots exceed that sum, i will pay for the £3.
Back to Coinery case, i remember there is no flat £3 option, and bidding through coinery website is less expensive than easylive portal. However, i am not sure about this now, coz i changed to bid through Coinery website since 2nd auction held by them because of the auction premium issue.