Don't drop a lot on this ring. If the price of the ring is a problem with her then perhaps you need to reconsider the engagement.
If the price of the ring is a problem with you, odds are she will reconsider the marriage in a few years as you probably are too selfish to make her happy. Many a divorced man has a $50k pickup, a $5k yeti collection, $15k in guns, and an ex-wife with a cheap *** engagement ring.
If you struggle spending 2-3 months salary on what should be a 50+ year purchase, you are either not with the right woman or are financially unprepared to get married. It's unfortunate, but you and her will be judged by the ring. Her friends will be talking **** behind her back about the ring either way. Make sure it's out of jealousy. Go ahead and get the nicest ring you can. Remember, you are getting married, half of what you spend on it is her money anyway. Might as well go all out on the one item she will keep forever. Best investment you will ever make.