Ain't that the most frustrating thing? I have an old Winchester model 57 sporter that shoots around an inch and a half at 50 yards. The exception is with one ancient box of Remington Kleanbore Match ammunition, probably 40 years old, which it will shoot into half an inch at that range. Nothing else. Not Eley 10X, not Federal Ultra-Match, not RWS. It's not for lack of trying to find something else as good, but it just doesn't seem to exist. It makes me wonder what Remington knew how to do back then that nobody knows how to do now? Probably older skilled labor retired and the "touch", never documented, was lost.
I'm guessing the best bet for reducing the cost of .22 Magnum rimfire is going to be to buy it by the case (5,000 rounds). I buy .22 LR that way. I wait for the Nationals to be underway and get it on commercial row at Camp Perry. where things are discounted. I wouldn't expect to find .22 mag in case quantities there, but I'm guessing you can special order it from a dealer and get a discount by offering to pay up front.