Here are some figures for the category "personalised mugs" for ebay .
Top seller (in terms of turnover) £969.00 (7days) price per mug £2.40 free postage
2nd seller (in terms of turnover) £833.00 (7days) price per mug £4.99 buy 3 get 1 free free postage
Its very tough, by the time fees postage and other expenses have been paid + manufacturing costs raw material costs, wastage etc etc its not looking good is it?