Here's the thing, you have your current vehicle paid off, looks like by your picture you have a lift and some pretty aggressive tires. If I were you rather than spending money on a different vehicle I'd look for some less aggressive tires and remove the lift, keep the parts of course, because you never know one day you might be able to afford to go have fun and want the lift and tires back on. Fuel economy suffers considerably when you are running with aggressive tires and a lift. Plus you state you have a 2.5L so that's not helping matters any for fuel economy you are working that engine trying to spin those heavy tires.
I have a full size truck I know what you mean by fuel economy problems and using most of your paycheck in gas $80 a week to fill up my toyota tundra, $54 every week and a half to fill up my 84 Bronco 2. So since I got the bronco 2 running I've been driving it and only drive my truck once a week or once every couple weeks just to keep it running correctly.
Something you may consider too, you said your mom has a 2WD ranger, if she don't work maybe you can swap vehicles with her as the 2WD ranger would be easier on fuel for you. Or park your truck and find a cheap car, I seriously wouldn't get rid of something that I spent all that time and money building to what I want.