The house repair bondo & fiberglass resin are exactly the same as the automotive label... The only difference is that the household putty has a different color creme hardner... One's grey, one's red. I'd hit Shucks, autozone, etc. though, as you can usualy buy the gallon size can for around $18...
I should have thought to mention it earlier in the fiberglassing threads, an old 'scifi-armorers' trick is to mix the bondo putty with the bondo fiberglass resin, I usualy use 1 gallon of putty to 2 gallons of resin, mix well, & you've got an awesome high impact surface coat, or even the entire glassing proccess. You use a shot of both hardeners ( the creme & the liquid), & it sets up into a hard shell in a few minutes... The putty addition makes the resin extremely less brittle. For thicker parts or reinforced interiors, I mix short-strand fiberglass 'chop' into the mix, then trowel or brush it into my molds.
I'll dig up & post some pics to clearify what I'm babbling about tomorrow...
Wolf