CD-WOW are having an up to 60% off sale until midnight tonight, which you probably already know. Found Mamma Mia DVD amongst the bargains - it's region 1 (USA/CANADA) but if your player is multi-region that won't matter. At only £4.40 it's a bargain but remember to get it before midnight! Not sure if money off vouchers work with this but worth a try, you might get it even cheaper!
MAMMA MIA DVD REGION 1 ONLY £4.40 DELIVERED AT CD-WOW UNTIL MIDNIGHT TONIGHT