Actually €80 or 85 at the airport for the first bag (op was asking Ath-lhr, not LHR-ath).

Also worth remembering that with economy basic, status related luggage benefits do not apply even if op buys luggage - so if op buys basic and purchases a check bag, they will only be entitled to one bag (23kg) even if they are owe. By contrast, if they buy eco plus with luggage included and are owe, allowance would be two bags of 32kg I think.