Passon 5 Speed

OK so I did some math... Since gas is going through the roof it is going to put a serious strain on me to keep driving my Valiant every day. I'll spare you the details but I drive about 100 miles a day round trip on my commute... Rough math (using an RPM calculator from Randy's ring and pinion site) says I can save $1500 on fuel in 3 years, just on my daily commute alone. Subtract 1500 from 4300 puts the price of that puppy back down to about $2800... Not to mention the wear and tear it will save on my engine on the highway... And then you throw in the FUN factor of bangin' gears in that rascal... which you can't really put a price on :) OK so what am I missing here, I think I have almost talked myself in to it... now I just gotta figure out how to pay for it...