I have an even cheaper solution: just don't buy a ring. It all depends on what your partner wants obviously. If it's important for your partner to get a diamond ring and you value your partnership more than the cost of a diamond, then buy a diamond. If your partner wants a "I'm married" sign (as my wife did), just buy a simple wedding ring without a stone. If it's not that important for her, don't buy a ring.
When I was still in the dating game, I wasn't one of the desperate ones who needed to f*k desperately at all costs. Rather I was every single time looking for potentially working relationship, so evaluating compatibility and if I found obvious or already-known showstopper I finished it quickly. But how do you evaluate that when initially people automatically wear layers of politeness masks? Some of them even after years.
Well just wait for first conflict and misunderstanding to happen, and how the other side reacts when emotions are high. Masks are off, raw personality comes forward in bad situation. You just have to be realistic and also think how it would look like if tables turned.
Or don't, but I prefer to at least try to bring some smart into this highly emotional game, I mean divorce rates hanging uncomfortably around 50% come from something (my wife doesn't have any natural bloody diamond on her ring, we talked about it like mature people beforehand and both agreed we won't go that way)..