Pretty much anything over $100 is out of the question for me, which puts a good chunk of the rare NES titles out of my grasp. I'll only own a Little Samson, Bubble Bobble 2, Bonk's Adventure or Panic Restaurant if I luck across one at a thrift store or garage sale. To put it into perspective, the going rate for Flintstones, Little Samson and the 3 Panesian games is $3,600 for those five games alone.
One of my best finds of the last few years was a Mega Man 7, which I snagged for just $5. I flipped it a few months later for about $60, but in the last two years it's skyrocketed to near $150 -- that's near Earthbound prices. Wish I'd kept that one now...