You could come back to "You get what you pay for" with "knowledge is power!"

Paying $3/lb for Sodium Carbonate, pH Up!, Balance Pack 200, is foolish when you KNOW you can get it for $.80/lb when it's washing soda.

Borax has several advantages over Sodium Carbonate.
It's less corrosive--on your hands it's gentler
It doesn't add T/A to the water
It adds borates to your water and borates inhibit algae growth.

Mainly, I'd shock the heck out of the pool, keep the FC level at the max for the CYA level.

Carl