Being Poor in Bloons Tower Defense 2 is knowing exactly how much everything costs. It's having to buy 30-point road spikes and 40-point monkey glue because that's all you can afford and you need something Right Now, instead of saving up for the 600-point cannon that you know you need. Being Poor on "hard" is always being exactly one level behind where you need to be. Being Poor is having no margin for error - make one mistake and you're doomed.
At least in a bloons game, you can just keep playing over and over until you know what's ahead, where to put every tower, and which upgrades to bother with. And then on Round 50 at the end when you suddenly don't need money anymore, it's disproportionally hilarious to cover the entire track in monkey glue.