XP BRU return question

I received two snug a bunny swings from BRU.  Not sure why but BOTH were shown purchased on my registry, yet I only registered for one....no biggie at all.  I want to return one to purchase something else.  Iknow for sure ONE has a receipt but the other I don't THINK has one.  If that is the case, how can I figure out which one to return since I obviously want to return the one that cost more.  In other words, maybe someone used a coupon and the other didn't, or one bought during a cyber sale, etc.  How can I find out how much I will get back before I choose which one to return?  There might be a 34 dollar difference if one of them didn't use a coupon.