If you are seriously worried about that, it's a huge sign you're not committed. Tiny resale value is preferable here.
Besides, depending on the cost of the ring, and the length of the marriage, it would make you more likely to terminate the marriage over time as the cost of the ring gets amortized over the length of the marriage.
http://en.wikipedia.org/wiki/Engagement_ring#Legal_ownership
Since you'll have to decline one of these proposals, one of them gets their ring back. Which one are you more likely to accept? All things equal, the 20k resale ring.