dual gastank rust, windshield>>ideas??

Okay, I have an '82 F-100 which is old, needs paint, etc. but I am keeping it - it has dual tanks, and my mechanic, after doing a bunch of work on it, says he put new gas filters inside the tanks, besides the filter at the carb. He said the rear one is full of rust... I moved quite a distance away from him, and I don't want to ask him, because I can't afford his work anymore, but... now I just fill up the front tank with 87, and it goes and goes... but I worry, 'cause I have to get to work EVERY day (they're sick of me missing as I wait for a tow truck...my previous vehicle was a '72 Superbeetle that had LOTS of rust in the tank... can I block off the line, drop the back tank, and get it cleaned, etc.?? and keep driving? I'd get a plastic one from J.C. Whipme, but I hear they don't always match up, and they aren't cheap! I need a quick, inexpensive solution - and I know - I should get BOTH tanks cleaned or replaced. I'm thinking of getting one from a junkyard, having it done, and putting that in... and the windshield is cracked...how much does a good glass shop charge for that?? sorry if I don't make sense - it's 5 a.m here in Georgia... this is a good group and thanks for any input... :+) Paul