As Mikaila said sodium thiosulphate is the active ingredient in most simple dechlorinators. If I had a source I might go that way. I find that the price per dose is best for me using Prime but the thiosulphate would be an even cheaper alternative if I had a source for it.
My water quality is generally pretty good during the summer, and I can get by with sodium thiosulfate during these times. Angels Plus sells the crystals, http/www.angelsplus.com/SuppliesWater.htm
I generally go with two drops per gallon of the suggested mix. The rest of the year, or if a storm rolls through that stirs up the lake I use Prime. A 2 liter jug gets me through the winter.