The cheapest mags on the market would be RAP4's Dmag. I havn't read up on how well they perform, never used one either.
I used to have a Gen6 T68, and it worked fairly well. It's just a STBB dressed up, so it's easy to fix and maintain. Mine worked well, though from what I've read on here most people avoid them.
There are also two new markers coming out some time this year, one from Milsig and the other Tiberius. Both seem to be looking promising.