One large beer keg should'nt cost THAT much...
And besides, even if they cost a lot, it's because they're made of Aluminum. Which does not corrode (aka rust) and flake of its hazardous oxidated pieces into the beer.
In the metallurgy industry, a pound of aluminum shouldn't fetch more than USD$9 and a beer keg should'nt exceed 15KG. Even if a keg weighs 15KG, I doubt it'd hit SGD$550.
I think it'll be easier to get the LPG tanks that you have under your stoves.
Check with the uncle if to see if it can be emptied and have it left in your possession for how much.