Okay not for everyone, as you have to go to Costco, but worth buying a couple of rolls as they should easily last you a year.
These are strong bags, I've been using them a few years and only has a couple split. As good as any other make and stronger than some. Brabantia rolls would cost roughly £25 for 100.
A cheap alternative I have tried are "Tesco Tall And Chunky Click Lid Bin Liners" 20 for £3 (ie £15 for 100)