Special diet for dog with urinary crystals...natural diet?

Hi

My dog has had some urinary problems over the last few weeks and the vet has advised a change of diet which he is supplying.

Unfortunately it's costing a fortune and not covered by our insurance (£32 a week).

I've been reading on a few American wesites about a natural diet and wonder what people's experience is of that.

I'll do what ever's best for our dog regardless of cost but to be honest I'm a bit wary of foods the vet punts when his walls are covered in advertising posters for them.

any suggestions or advice would be most welcome.