Chlorine--Regular or Ultra unscented, non-sudsing, non-gelling bleach--Chlorox now has an added whitener that MAY or may NOT be good for pool water--so stay with the house brands. Liquid Chlorine (LC) at the pool stores can be cheaper or more expensive.

Regular bleach is 5.25% If the pool store LC is 12% and costs no more than 2x the bleach it's a good price.

Baking soda? Any brand. But the pool stores sell it as "Total Alkalinity Raiser" and it's insanely expensive that way--and still only baking soda.

Washing Soda: This is the same as Soda Ash or the pool store "pH Up!" or equivalent. It's the same stuff. Arm'n'Hammer sells it in the YELLOW box (not orange) and it's in the laundry section, usually next to the Borax. It's super-cheap--less than $.80/lb here in NJ.

Borax: The only kind I ever see is 20 Mule Team Borax. It's for raising pH but doesn't raise Total Alkalinity the way Washing Soda does. If you have Borax and Baking soda, you don't need Washing Soda.

The ONLY things you can only get from pool stores or the pool sections are:
Stabilizer or CYA (Cyanuric Acid)
Dry Acid (powdered pH lowering)
PolyQuat algaecide (the only type of algaecide we recommend).