I think it totally depends on your interest level, budget, plans for collection size, place on the learning curve, etc.
I sample something new almost every day, then I try to get decants through swaps, so at least 1 package (2-3 frags) of those a week. I maybe buy 1-2 bottles a month max, but personally I really plan that my full wardrobe will end up looking like 20 or so bottles, 20-30 10-15ml decants, and 50 or so samples for reference or to use here and there. That's at least MY endgame plan, but I've only been at this around 6 months, so totally up to you. For me, spending max $30-40 on a frag I can tolerate 1-2 a month for a few months.