i beg to differ. My compressor paid for itself in the first year and a half, and at a cost of around $2.00 a fill vs $10.00 a fill it is still today an excellent investment. Let alone the fact that no one in my county offers nitrox. I would do it the same way all over again.
Glad it's worked out that way for you.
Compressor + Booster + Storage bottles + Filtration + Hardware + Mixing gas itself > $8/3L Oxygen fill & $15/3L 10/50 Diluent fill for me.
It'll never pay for itself, but it sure makes life easier. (I know that some evil shops charge $10/fill for gas, but that's insane.)