Water leak around tub surround. Suggestions?

Hi folks-
My upstairs bathtub area has a leak, that is resuling in some water dribbling down behind the tub tile, wetting the floorboards, and working it's way down to the ceiling of the downstairs bathroom directly beneath it.
The water is coming from the general area of the front of the tub (where the faucet and handles are). I removed the access cover and found that the 36 year old tile around the tub is affixed to common drywall, not durock or other waterproof backer board. Crap.
Despite a recent recaulking with silicone sealant, water seems to be getting through the caulk/grout seams, soaking into the little metal "tray lip" of the tub that the drywall sits in, running down along a very slight incline in this lip to the corner, then dribbling down to the floorboards from there. Water also is seeping in around the holes in the tile/drywall due to poor joins between the plumbers putty and the rotten drywall (yuk!!).
I recognize the right fix as being basically a gut job of the whole tile/drywall backing, replace with cement board, and retile. But we've got houseguests coming in two weeks, a baby on the way due mid August, and a tight budget.
What I'd like to do is put this off for a year, if I can find a way to hold back the water.
Any thoughts here? I can re-grout, re-caulk the area in question. That's easy, and may reduce water infiltration. But more is needed. I had some thoughts of chipping out the crumbly drywall behind the bottom tiles where the worst of the problem is, and using mimimal-expansion polyurethane foam to fill the gap and create a (relatively) rigid, completely waterproof backing for the base of the tiles where they meet the tub.
Suggestions appreciated!
Sincerely,
Marc
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If you're only looking for a servicable fix and not a pretty fix, why not buy a fiberglass repair kit and put a layer of fiberglass cloth and resin over the entire mess?
KB

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Use a grout saw and regrout get all the loose stuff out. Remove old caulk with sharp razor blades and recaulk with silicone, remove handles and be sure all is sealed behind them. I wouldnt remove any backing or use foam.
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<< Despite a recent recaulking with silicone sealant, >>
Other sealants will not bond to silicone, so when you do your temporary patching you're pretty well commited to the same thing. Where you have unsiliconed surfaces anything should work. Try to expose the old plumbing as much as possible to observe water leakage during use of the tub, then correct by whatever means necessary. You may need new faucets, drain, whatever. Good luck.
Joe
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