If money is going to be tight, and if you don't get enough money from the sale of your explorer to buy the car you want, then you will have to take out a loan, which means a car payment plus gas, then it will likely cost just as much, if not more to buy the car that gets better gas mileage. The only time I've seen this work was when a buddy of mine, he drove a 91 K1500 GMC 4x4 with the 350, averaged about 10 mpg. He kept the truck (was his dads and can't for the life of him sell it), and took out a loan to buy his moms toyota camry 4cyl. He went from 10 mpg to about 40 mpg. He was driving over 40 miles one way to work. He figured it out, he saved about $50 a month by buying the car and taking out the loan. When he did this, gas was about 2.75/gal. He went about 400 miles/week just for work, in his old truck this is 40 gals. 40*2.75=$110, then multiply it by 4 weeks is $440 just in gas. For the camry, 400 miles, is about 10 gals, 10*2.75=$27.50, times 4 weeks, $110 a month for gas. His monthly payment was about $300. 440-110=$330. Again, this is just going back and forth to work, and shows that there was not that big a savings. But he had a sever case of really bad mileage, to a vehicle that got really good mileage. But going from an explorer to something that gets similar mileage is not going to show the same results. You would have to drive way more than the 80 miles a day to show any kind of results.
Dan
If you still have stock equipment you could try putting it back on and selling your mods separately. Might yield a bit more money. My buddy had a highly modded '03 cobra vert and did that, ended up getting more than he though he would. And yes, I'm aware that a cobra is a little different than an explorer 
