I used to sell jewelry (etc.) at Macy's in high school/college and at Kreigels/Hannoush (regional chain store) while in law school. I looked at 40 stones before buying the one I bought. You have been given good info re educating yourself re Cut, Clarity, Color and Carat Weight. I offer the following:
Executive Summary-the easy choice is Costco or a local multi generational family owned store with an excellent reputation.
Costco is knocking it out of the park re the quality/value intersection. They are also a leader in selling rings that have been set with a stone in the center surrounded by much smaller stones surrounding the center stone such that the ring looks like a much larger solitaire from just a few feet and beyond. i.e. the center stone is .82 carats, the surrounding stones make it look like at 1.25 carat ring. The Costco ring is 3000. Any decent 1.25 carat solitaire would be 2.5 or 3x that all day long.
A locally owned family stone often carries a certain panache that can have real value to your wife. The panache can extend outside of the local area. One three separate occasions when my then wife was traveling to Las Vegas, Chicago and New Orleans, she had her ring cleaned at a local store. When asked where she was from, she said KC. The jewelers then asked if the ring was purchased in KC, she says yes. They then ask, "is this ring from Tivol?" Tivol has a national reputation in the trade and simply does not buy poorly cut stones. Tivol is one of the oldest family run stores in KC and Tivol grand kids are now in the sales force.
Another sure bet is Tiffany's. You will overpay relative to the other two choices but there is an undeniable snap of the blue box. Tiffany jewelry is a lot like Rolex. Superlative in quality and the price reflects that.
1. Do not buy anywhere that you cannot get a full refund are at least a full in store credit.
a. She could say no
b. She could change her mind
c. You could change your mind
d. Another ring could come on the scene
e. She might not like the ring
2. Find out what she wants re shape and setting
3. Put your money in cut first and color second. A well cut, whiter stone ( G or better). By analogy, well tailored suit looks better than a less tailored one, This is often true even when the less tailored suit is of better fabric. Cut is everything. I would buy a well cut 1.0-1.2 carat stone with decent color way before a 1.5 carat stone that was not as well cut or white at the same price point.
4. Do not forget to call your insurance company and have it "separately" scheduled and covered for all hazards to include lost, damaged and mysterious disappearance. Most standard insurance policies cover relatively small amounts re jewelry, subject to your deductible and do not cover all hazards.
5. Unless it is an heirloom, there is always another stone out there.
6. I would ask about a cash discount. By definition it should be at least 3% as that is what a credit card company would be charging the store to process the payment.
It is always possible to find well cut, quality stones from a pawn shop, chain store etc. In my opinion and experience, it is simply much easier to do so at the places outlined above, stone for stone, day in day out absent some kind of association you have to a decision maker at a pawn shop.