I've used $20 shampoo, and I've used $2 shampoo. It hasn't been the price that made the difference. If you're the kind of person who likes to experiment, try different products ---- I'm a fan of the "Yes to" line (carrots, cucumbers, etc.). Also, you may stumble upon "high end" products priced less expensively in surprising locations like Marshall's or T.J. Maxx.
However, if you're very happy with Deva, you're pressed for time more than $, and you're not the kind of person who doesn't mind unpredictable results, I would stay with what works.
Dogs and nature abhor a vacuum.