the only thing i buy monthly is 5lbs of protein for ~$30 (just get whatever is on sale/cheap) and take around 2-3.5 scoops on workout days, and 0-1 on non-wo days
other than that, i buy supplements whenever i have extra money (at the end of last month i spent $80 on no xplode, noshotgun, and fish oil... which should last me a while, especially on preworkout)... a couple months before i bought some daa/inhibit-e to save for a rainy day).
im starting to get a little ahead of myself as my protein usually lasts a little more than a month, so after i order my jug this month, i THINK i'll be held over until october (ive got like 20+ servings left in the jug im on now), so in september ill spend that $~30 on some titanium to put away for that daa/ie stack (and im hoping to get a little extra this fall/maybe Christmas to get some anabeta for that stack too).