Canadian looking for salt

[giroup01]

Anyone know where I can get the salt (cheap) to start up my SWG.
Pool stores want $32 per 80lbs bag. I apparently need about 350lbs. Is that a reasonable amout to pay?

Thanks

Rona, Reno-Depot, Home Depot.
About $4.00 CDN for 20 kg of water softener salt.