I have a $50 (US) monthly budget for "Innerdude gets to spend on whatever he wants." The catch is, it's for everything. Board games, video games, PnP RPGs, Kindle purchases, random trips to Chick Fil A, it all has to come out of the same pot.
As someone said earlier, if there's not a 100% chance it will actually get used at the table within 18 months, it's a hard pass.
Plus, there's only so many rules systems that one person needs. I basically have my eye on 3 systems currently: Swords of the Serpentine, Dragon Prince (the Cortex Prime system), and Spellbound Kingdoms.
After picking up those 3, I honestly don't see myself buying new RPG material for a long, long time.