Save up, pay for it with money you have. You never know, in the time it takes to save up for what you think you want, a better deal, or a change of heart may come along. I was building a stand-alone fuel system and about to direct-port N2O my car when a deal on my procharger happened to come along. For what I had saved to do my N2O upgrades, I bought the D1SC for. Sold all my nitrous stuff and used that money to buy my fuel upgrades.
The other shitty thing about financing FI, is if you are financing it, you basically can't afford it. Like it's already been said, if your motor lets go you're down 'til you can afford a new one, on top of financing a blower kit. Beyond that, whenever I've done work to my car, other shit always pops up while I'm doing the build. A set of gaskets here ($) extra hardware there ($) a tool I didn't have and had to go get ($$) and then damn, forgot I had to tune it as well ($$$). I even went out of my way to do a major brake upgrade to the car, because the stock brakes felt severely underrated for 450whp. Quite honestly, I didn't feel safe going to the top of 3rd anywhere.
Sometimes, doing things right means you have to have patience. Makes it all the more worth doing, when it finally happens.
