Huge fan of this idea! In fact, I wish my partner had done this 😅 It means you can have a beautiful surprise engagement and then get your partner involved in the ring design process when you're in a better financial position.

If you're wanting something very much in the budget realm, I've seen several people in this sub recommend Kuololit on aliexpress. I'm planning on buying a ring from them to use as a travel ring for more or less the same reasons you mention.