I'll be keeping my eye on this because I love Carefresh but like you say it's really expensive. I've tried loads of different things for litter and this has been the best. My two just wee and poop so much I have to change litter twice a day making care fresh cost about £20 a week for us as a minimum. So at the minute I'm using chopped straw, not absorbant in the slightest but super cheap!
Haven't seen it any cheaper than Pets at Home so can't help you there.