I check my dry cat food prices at Tractor store vs Amazon ( if you have Prime, it ships free with no taxes), so I order dog dry and cat dry there, making sure it meets urinary tract guidelines for male cats.
Other option is wal-Mart but I use a higher end dry food than is usually available at Wal-Mart.

You can also search for "Cat food ratings"
I found this under "cat food advisor:"
http://www.catinfo.org/

The problem is that Royal Canin is available only with a vets rx. After I posted the OP, I did find chewy.com carries the same RC, but I have to have the vet fax the rx first, then call the next day to order it for delivery later in the week; by the time I add the cost of the vet rx fee (brand freaking new and I'm peeved about it) and shipping, it is the same cost as buying it at the vet.
The bladder stone was in the mom cat, which was a big surprise. That catinfo site is pretty good isn't it?

Thanks for replying.

and vet told me the whys and hows of the problem, which has to do with not enough ash or something in feeding only dry.
I feed both wet and dry now to my cats, have never had the problem again.
My guy is 13-14 years old now, and thriving.

The "indoor" named dry is esp. formulated for urinary health, but there are other dry foods that have the same ingredients, you just have to get good at reading labels, which the internet is great for!

The canned, which they love of course, is just a couple of tablespoons in am and pm,plus they get dry food in a bowl.
So they have mostly dry, then whine to get "dessert".
It is a LOT cheaper to get a good dry food retail, and even better to have it delivered with free shipping, IMHO.
But we do not have access to city shopping with lots of different stores.

If you have a dog, dogfoodadvisor.com is a great site, they break down all the foods available and rank them in terms of quality.

You don't reveal which Fromm cat food formula you are considering though. In my cat food pantry Fromm four-star dry kibble is on the fourth shelf down, two formulas Game Bird, Chic Ala Veg. On the upper shelves we have the favorites, Acana. Second shelf has the Pure Vita. Third shelf down is the Halo Spots Stew grain free. Not long ago one out of three of my cats would commonly suffer bloody symptoms of UTI's every year starting late March and continuing through late June. Six years ago I started adding canned food along with my home made Chic, Turkey and soft cooked egg & fish soups to every feeding. Now over 5 years I have had only one cat with confirmed bacterial bladder infection. No more feline interstitial cystitis at my house. My kitties though are now mostly seniors, youngest three are 9 yrs old. As for Royal Canin, I have a very low opinion of it. As for the prescription Veterinary diets, I have in the past only used Sci Diet CD/SD for short duration. That SD formula has worked very well on two of mine that had confirmed large stone. Never had a cat with oxalates, but have had many many instances of struvites. With two male cats the Dr warned me to keep up with the prescription diets but I never did. I just added a lot of "wet" food to the cats diet instead. I like the Fromm product first because all the cats like it, it remains a family owned business, not had any recalls that I know of. What I do not much trust any pet food producer is on their sourcing of quality ingredients. Fromm has a nice loyalty or freq buyers program too, buy 12 and the 13th is free. I'm not bringing in the 15 lb any more. The 5 lb is $18 - $22 today, 15 lb $36 - $44.