I'm not really poor, but I'm certainly not rich... but there are a few "free to play" games that I play so frequently and love so much that, when a great sale comes up, i spend some money on it. For me, that WAS Castle Clash, and currently is Summoners War. Castle Clash kept me entertained for almost two years, and I recently found myself dusting off my old account and enjoying it some more. Summoners War I simply appreciate that when they say "free to play", they mean it... you can reach all levels of end-game with easily obtainable and farmable units. Plus, they both play on a gen 1 IPad (unfortunately, Fallout Shelter does not... thus, I can't add that to the list, though I probably would).
How about you?