There are a number of shops spread around the valley. I am fairly new so I can not say what prices are good and what are not. But most of the stores are worthy of return trips. Google Saltwater fish stores in Las Vegas. Then start checking them out.
Aquatic Treasures is my absolute go to !!!
Trop Aquarium is good but can be pricey
Same with Pisces Reef Emporium
Blue Reef Aquatics is pretty good but far north
And Reptiles and Reefs are ok for some supplies not much livestock
I think it was Pisces Reef I went too recently, they are closed.
Aquatic Treasures is very nice, fish coral, no sps. The lady is super nice and thankful for the business. Their livestock is very healthy.