A 2004 Ford Expedition gets 13-15 mpg in cities and 17-19 mpg on the highway. I’ll estimate that yours gets right in the middle – 16 mpg overall. If you live in an area with gas at $3.50 a gallon and are spending $400 a month on gas, that means you’re putting about 1,800 miles a month on your vehicle – $400 divided by $3.50 gets you 114.3 gallons of gas a month, and at 16 miles per gallon, that’s just about 1,800 miles.
So let’s go with that. Let’s say you replaced your Expedition with a 2008 Ford Escape Hybrid, which gets 30 mpg on the highway and 34 in the city, so for you we’ll average it at 32. I chose the Escape Hybrid because it’s comparable to the original in size and storage which you probably still need, but much more fuel efficient. If you drive 1,800 miles a month, that means you’ll only burn about 56 gallons of gas with this model versus the 114 gallons you were burning with your old one. That’s a savings of about $200 a month – you’ll basically halve your monthly gas bill.