It usually isn't cheaper than TJ - in fact I'm not sure I've ever seen anything there cheaper than TJ.
There are a bunch of pharms on the main drag but I'm not sure about vets. I know there is one on the out skirts of town near San Miguel, but he doesn't have a great selection.
There is a cruise ship terminal at the port there so everyone that comes down there is typically older and has more money, the pharm get less traffic than TJ, so they can't go as low on the prices.
If you need a well priced vet PM me it's in TJ and they carry everything and they cater to BBers.
Anyway, just my observations and experiences.