Use RO water and add your minerals, this way you have full control over your water.
RO water is $1 per 5 gallons at my local supermarket (http://glacierwater.com/
), but I don't know the availability of your area.
Don't waste your money on 5.2 stabilizer, brewing salts are dirt cheap.
Start at the primer and work from there:
5lbs (~$10) of acid malt (sauermalz) will last you ~10x 5gal brews.
Minerals used: calcium chloride, gypsum, and epson salt. 1lb of each will run you <$10 and last you many years if kept dry.