Terrible Gas Problem with '89 Camry

[Adeline7]

I bought this 1989 Camry last summer, and after a few replacements and tweaks, it ran beautifully. I got 30+ miles to the gallon on the highway. I get about 350+ miles for a full tank.
Lately though, the mileage has been awful. I drove about 70 miles on a full tank a few days ago, and I ended up with half a tank left! I drove another 40 miles the last two days, and my tank is nearly empty. I'm not sure when it started, but it seems to be getting worse. Sometimes, after I've driven the car for a bit and I park and get out, I smell gas, but only briefly. I haven't smelled it lately. I've put a piece of cardboard underneath it after driving and caught a puddle of gas on it, but it was only the size of my palm. Would this cause such a drastic drop in mileage?
I had my uncle look at it and he apparently found a leak near the breather tube of the gas tank, but he said it was so small it shouldn't make this big of a difference.
For a while I smelled gas in the car, coming from the vents. My mother and the man who sold the car to me took it for a test drive one day and both claimed they saw fuel coming out of the fuel injector, but after my uncle popped a loose spark plug back in, no one has seen fuel from there, and I haven't smelled any IN the car.
My dad's mechanic said the fuel filter might need to be replaced because the car idled low.

What in the world is wrong with my car? How much would it cost to get this checked out and fixed? I can't afford to take it to a mechanic at the moment. Can I fix this myself?

[white90dx]

If you found ANY fuel leaks, that's a huge problem. Figure out where its leaking and fix it.

It sounds like the leak is somewhere on the pressure side of the system. When the car is off, it won't leak (or at least, not much). When the car is off, you have ~45psi of pressure in thsoe lines and it can cause major leaks.

-Charlie