Bath/grooming products for sensitive skin

Hi! My vet thinks that Summer has allergy issues and is recommending that I bathe her every 7-10 days. I have a medicated shampoo he has given me but it is kinda pricey so I wanted to see if anyone had recommendations for other very mild products that I could buy when I run out of this that won't be irritating to her skin especially given the frequency of use. I have been wanting to order some sort of spray to help with shine for her coat but I am nervous to put anything on her that she doesn't "need" for fear of it causing irritation to her skin. If anyone has used something for this purpose on their pup with allergies please let me know what you used, thank you!!!

Mine don't have allergies, but if you're looking for a mild shampoo for frequent use, my lot get washed in Chris Christensen day to day shampoo and conditioned with day to day conditioner. I see they also have colloidal silver sprays and gels for allergies and hotspots too.
http://www.chrissystems.com/all-natural-pet-skin-problem-solver.aspx
How much does your vet charge for the medicated shampoo?
Sins