I have used my box of Borax for over 6 months and I still have half a box left. If you are unsure, check with the manufacturer to make sure that is is safe for your appliances. In my humble opinion, it is better than the commercial products.
Have you tried Borox? A large box at my grocery store was about $4.00. I use it to stretch my laundry detergent by cutting the amount I use in half using less and adding a little Borox.
You can also use Borax and a little Baking Soda to make your existing dishwasher detergent last longer too.
Here is an easy method for making your own dishwasher detergent. This is a cheaper and “greener” way to go. Use one tablespoon of Borax and one tablespoon Baking Soda in the detergent compartment, that’s it!. For a rinse agent, use white vinegar.