So I think I'll go with flexwatt + 500R until I can afford a proportional therm.
Things are a tad too variable, and I want to be able to dial my temps in for my little buddy.
Just got my 500R the day before yesterday. It took some tinkering to get the temps to level out but it has maintained a solid 91.5 degrees for 2 days now with no more than a 1 degree difference up or down. It really is a decent piece for the price.