I would say you need to read the labels. I was doing a service just today and my long time customer showed me here chemicals and asked that question.
So i showed her the labels on her Walmart brand stuff compared to mine the Leisure Time line. While my Dichlor was 99.0% real chemical hers was 44.5% actual dichlor, same with some of her other chems.
So ... if you compare the small price difference to the huge real chemical difference -- my stuff was quite a bit cheaper.
Thats why when you purchase quality chemicals you dont need to use as much either. The other issue is sure your getting a lot less real chemical --but your getting A LOT MORE FILLER CHEMICAL, or what they call INERT INGREDIENTS . This can actually be counter productive when it comes to safe and clean water chemistry. SO NOW -- TELL ME -- is that $2.50 cheaper bottle of brand X chemical really cheaper?