1993 Buick Century Gas Leaking

I will be seeing my mechanic today about gas leaking from my vehicle. When I filled it up last gas started pouring out underneath the back of the car (rear drivers side tire). I also am seeing fluid (gas?) Spillage along with rust stains where I park my vehicle. My Dad (who lives in FL and can't physically help me) said that you can purchase gas tank patch kits. I am on a really tight budget and this vehicle was purchased for me, by my parents, to replace a Saturn that was constantly having problems until the engine actually died. I am looking for the best inexpensive fix. Would you suggest the patch or trying to purchase a new tank from a "junk yard". My mechanic said he had never heard of the gas tank patches before so he would be new at using this technique. Any direction or suggestions are welcome. Thanks!