Well, the real difficulty here is finding a cheap source of ammonium thiosulfate (the active ingredient). As I understand, dry ammonium sulfate doesn't keep well, so it's usually sold in solution (about 60% IIRC). Sure, you can buy either of these, but the consensus seems to be that it's cheaper to just buy the finished Ilford product than it is to source the ammonium thiosulfate in most cases.
It actually keeps reasonably well, but a small percentage tends to sulfur out. This can be filtered out after dissolving the dry crystals.The stuff does have a way of clumping and should be stored in an airtight container. Dry ammonium thiosulfate is fairly easy to purchase, but for a private consumer, the price level may not be very attractive when compared to buying ready-made fixer in somewhat lager quantities.
This is indeed a quite effective and affordable way of making fixer. But it doesn't allow a very high concentration like with actual ammonium thiosulfate. I don't think it's feasible to make a concentrate for e.g. 1+10 dilution for paper processing this way.