A lot of the posts in here point to a greater problem which is the fact that "she" is concerned with the cost of the ring. Really it shouldn't matter to her so before going on; think that through.
I did the 3 month thing (but with my frugalness ended up at 2 months!), which was more than she was expecting. It turned out to be about 4k and that was after I went to the states (from Canada) to buy the same ring from Michael Hill for 2k less than in Canada. (Would have been closer to 6k mind you the exchange was better at the time).
Here are my thoughts... take her to a jewlery store. Don't online shop. Let her see it on her finger. It baits the hook but allows you to set expectations.
Also...you get a feel for what she likes.
If she's comparing to friends and stuff....don't win on price/cost. Win on design. Get a feel for what she likes and then do up a custom ring. Uniqueness could win her over. Some places like Michael Hill will allow you to get different sizes of the same design for budget. I know for a fact that down the road I'll upsize her on a major anniversary. Michael Hill will credit the original value of the ring too which is nice.
There are also ways of cutting cost. What's important to her? Size, clarity, a perfect diamond? You can skirt a bigger diamond if one of the facets has a nick in it.
Cost is a talking point sure, but in the end a pretty ring will catch someone's attention more. There are some pretty gaudy rings for money. Feel her out on what will truly make her happy. If it truly is the money...well revisit your process. Maybe she should buy you a ring
