My boyfriend feels bad that he can't afford to get me a promise ring?

You don't need any help, you two seem to be in an understanding relationship, and you weren't angry with him when he said he couldn't afford the ring. I don't see why you need help

What is he considering to be a promise ring? If he really has his heart set on getting you a ring, there are lots of possibilities. What would you think of a silver ring? Silver rings are really inexpensive nowadays. If not silver, have you thought of checking out your local pawn shop. Yes, these rings were pre-owned but big deal. Those shiny new rings in the store have been on the fingers of a lot of people who are trying them on. Hey, a friend of mine still chuckles and tells her children about the plastic ring their father gave her from a candy machine for 25 cents because he had no money.

You don't need a promise ring to show how deeply you love eachother, objects are nothing when it comes to love x

If you say it's OK and he doesn't believe you, then you're going to have relationship problems a promise ring wouldn't solve anyway.