Welcome to BaB Rob

Best way for you to gauge actual price being paid, is through comparison. Finding similar mountings and comparing prices between them. Most basic solitaires are rather similar and stores you are shopping should be able to give you a weight to help compare "apples to apples".

You'll find both reputable vendors online and locally. The thing that you need to take into consideration is the level of "service" you are going to be comfortable with. A basic solitaire with a CZ or other synthetic isn't really going to be a challenge for any jeweler so "quality" wise you should be able expect "similar" things regardless of where you go. Remember, things like sizing, stone tightening, cleaning and inspecting can come with additional costs so be sure and ask about it.

However, regardless of where you decide to make a purchase, future considerations will come into play. Things like where to have it inspected. Where to have any alterations (eg sizing) if and when needed. Where to ultimately purchase your diamond and have it set. Keep these things in mind and ask questions along these line as you're shopping.

Hope this helps!