Based on the numbers you provided it looks like your commute mileage for the year is about 1250 miles and on an annual basis your HAH is averaging about 26 mpg. That means you are using 48 gallons of gas per year to commute to and from work. If you switched to a Prius and managed to average 50 mpg you would consume 25 gallons of gas per year just for your commute.

Fuel savings is 23 gallons annually or $69 assuming $3/gal. Unless it's not going to cost you money to switch to a Prius I hardly see the point as your fuel cost is less than peanuts compared to all the other costs of vehicle ownership. Heck, you could drive an H1 at 10mpg and fuel would still only cost you $375 per year.

If you just want the SMUGness associated with driving a 45-50 mpg vehicle that's one thing, but switching does not seem to make sense from a purely financial perspective, IMHO.

Addendum: If you averaged 125 mi/wk, your annual mileage is 6250 and, assuming the same fuel economy as above, the HAH would 240 gal vs 125 gal for the Prius. Again assuming $3/gal the reduction in fuel use would save you $346 per year.