Getting back to the original question... I'm pretty sure that I'm an exception to the average case, but I tend to spend in the $25-50 range out of pocket for each new set that comes out. I supplement that by selling pulls/packs/mats that I win each quarter, and by judging in multiple leagues, and by TOing Pokebeach tournaments.
I also cater my decks slightly toward what I can build without breaking the bank (so, for example, right now I still have zero Rayquaza GX and I have only a single copy of Blacephalon GX which was obtained before the price spike, costing me around $11). If I need expensive cards to be competitive, then I will get them. But most formats have a few mid-tier options that are actually very strong (examples include Bulu and Solgaleo in the Garde formats, Silvally Boxes in the pre-baby-Buzz formats, Psychic Malamar while baby buzz and Buzz GX were at their height, GasKan last format, Decidueye/Zoroark and Granbull in the current format).
Nice, those values are useful for me to set a target and see if I'm doing over or under. Since you're also making money from your hobby, does getting better GX's treated as a ROI? For example: If I pay 50$ on those 2 cards, I have better chances to get a nice place on this championship and score more prizes to sell/earn.