This sounds very familiar to a recent post... I'll repeat what I said on that one:
According to everything I've read, urinary care foods have a reduced amount of phosphorus and magnesium, which both contribute to the formation of crystals. The level of acid in the urine is decreased which therefore increases the ratio of alkaline which is what helps to actually dissolve the crystals.
But, there is no where you will find that increased water intake is not essential to this process, and so obviously canned food provides more water than dry ever will. Most of the web sites of the companies who sell urinary care food stress that increased water intake is a definite key to reducing/eliminating crystals.
That is simply because the added water causes more thorough flushing of the urinary tract, and whatever crystals that are being produced are flushed out rather than being allowed to propagate in an acidic environment. Less crystal formation means less likelihood of infection and blockage.
To me: more water = less acid = more alkaline = less crystals. Adding the urinary care food just helps speed up the process be cause it removes crystal producing phosphorus and magnesium, while reducing acid and allowing more alkaline in the urine to help dissolve the crystals.
Oops - When I went to search for the other post where I had responded - I found it was posted by you too!! Oh, well - here it is again.
Don't know where you are located, but I get the RC SO in both cans and dried at PetSmart. I believe a 7.7 lb is around $37, and I think it is between $1.50 - $2 a can. PetSmart will 'renew' my prescription automatically for me even though I don't use them for pet services/vet visits.
There is also Hill's C/D dried and canned available - about the same price range as RC. There is also a non-prescription version - Purina Pro dried and canned, which I believe is less expensive. I have also heard of Wysong Uretic (also non-prescription), but I am not sure if it is also available in canned.