As far as I know u could technically use BM bags again but they would use there sterilization benefit. I bought lasinoh (sp?) bags of eBay for really cheap I think 50 for $15 it was a uk seller. Otherwise someone has suggested to me there are freezer trays that freeze them in cubes of say 30mls? I think u would be able to freeze them and then maybe transfer to a normal bag and keep reusing the tray?

I just use the bags but others may have handy tips