If it's struvite crystals (and not calcium oxalate crystals -- very different and the treatments are opposite), before you switch to the crappy food, try these steps:
1) start giving the dog distilled water only. Sometimes dogs develop this problem in one home as opposed to another simply because of the minerals in the water supply. (The sort of thing that gets picked up when people move, or a show dog lives in different parts of the country at different times of the year, etc.)
2) Add a spoonful (I used a T for a 50-100 lb dog, but if yours is smaller, check with holistic dog websites for dosage) of apple cider vinegar to the food or water (whichever the dog prefers).
This alone may be enough to regulate the pH. Get some test strips from your vet and see if you can get it into the correct target range.
When I suggested this approach to my vet, he agreed it would work, just that "most people" wouldn't make that extra effort. Really? A tablespoon of liquid from a jar on the counter as opposed to switching to the equivalent of floor sweepings as a diet? I think most people are capable of that amount of effort!
This approach was successful for me and many friends in the show community. You do need to monitor the condition, of course, because the crystals can cause UTIs and eventually other problems if they are not managed.
To clarify, there are conditions for which prescription diets are your best option, but run of the mill struvite crystals are not one of them (at least not before trying holistic treatment)