If by "salt pool" you mean a pool with salt and a SWG to produce chlorine, then the chemical costs on an average month will be very low. Mostly you tend to need some muriatic acid, probably one gallon at around $5. Then you might need a pound or two of baking soda, $1.50.
Then there are a couple of things that are only required perhaps once or twice a season. Spreading them out over the season, one month's worth might give you 20 lbs of salt, $2.50. 1 lb of CYA, $3. Two gallons of bleach $3. One cup of polyquat, $5. If you have a plaster pool then 5 lbs of calcium, $7.50. If something goes wrong and you get algae once a season, then another $3 of bleach.
All of this is approximate and will depend on the size of your pool. The first month's costs will be higher as you need to add a lot of salt to start.