[LasciviousXXX]

Well, a standard 1.5 carat solitaire w/ a clarity rating of SI1-SI2 with a color in the G-H range will run him around 14k-18k at most of your box jewelry stores (Kay, Jared, etc) . Obviously if he wants to step it up to a VS status and F color it will increase in price exponentially. Best idea is to have a friend who actually works in the jewelry business so he can get you a decent price on the perfect loose stone first, and then choose a setting second.

However, if he doesn't know someone in that industry, best practice is to spend a week or two going into various jewelry stores and taking 20-30 mins to talk with a salesman about what he's looking for and what they have to offer. Places like Tiffany's & Cartier have big names that his fiance will recognize if she's into that. Both good places to start.