I have feeling that an event I used to involved with looked into getting mugs done, think most places the minimum order was 36 & think they were looking at about a fiver each at that order level, not sure wo they used but think they looked at company's like hotline.co.uk, 4imprint.co.uk plus others who I can't remember, not sure who they used in the end, might also be worth looking if you have a local corporate merch supplier