[The Bard Rocks]

Denise and Capt. Jim have given you excellent answers - your marriage should be worth more than a guitar. That cuts two ways: he needs to realize that his marriage is worth more than the cost of a guitar for you.

I'd try to rouse some enthusiasm from him if you can, get him involved in the selection process. You need another's ears anyhow. If he becomes part of the decision -making process, it will be easier to agree. Ask for his help (listening to how it sounds, bargaining, finding the right place to buy it....) and bring him into the process and maybe he'll garner enthusiasm he now lacks.