2004 Dodge Intrepid Gas miliage out of Control

My 2004 Dodge Intrepid is burning gas at a very high rate. I put in half a tank of gas, and by the miliage I wrote down and notes on when the needle moved, its getting anywhere from 3 to 5 miles to the gallon. Every day I have to put more gas in it. A mechanic I took it to said it needed a regulator in the gas tank. It might be stuck. I just put in a new alternator and I don't have the money for the regulator and labor, which is 100 an hour. If I can do something myself at home, that would be a blessing. It is up to date on oil change, and tranny change. It had been doing this for about 4 mos. But not as bad as this. I would appreciate any advice on this. My husband was a mechanic with 25 years experience, and he would have known what to do. He recently passed away and I feel I am being taken advantage of at all these garages. Thank you for your time.