If you really want more money in your pocket, sell the FiST and buy a used car for under $10K. Lots of fun performance cars at that pricepoint and lots more money in your pocket to mod them.
Don't ever go to a dealership to have them "crunch the numbers" for you. You will lose every time.
$100/mo = $3/day or $1200/yr. Quit going to Starbucks and you can about cover that cost.
A Honda Fit? Something tells me you will be willing to pay that extra $3 a day when your invisible turbo doesn't kick in.
Good luck. I suggest you find a friend with a good handle on their $$ to help you make the decision.
Source: I work in finance, and our main goal is to get you to spend more $$$.