FF an update/alternative on your research and thanks for a great post. I was after the 3M 7502 as well with the same cartridges you mentioned. PaintAccess has a special with the 7502 plus the 501 cover and filters and cartridges for $55 delivered to Victoria. The cartridges and filters are not the 5925 and 6051 but you can buy a pack of them at Bunnings for $24 which includes a pair of 6051 and two pairs of 5925, which is a year's worth. No need to tie up your money buying 10 pairs.
So in my case that's $79 in the first year and $24 per year after that. I find that quite reasonable for good A1P2 protection.
When I read your figures I was concerned how much this was going to cost me, particularly in the first year, but It was that pack at Bunnings that eased my mind. I hope this helps someone