Engagement rings actually were a marketing scam, but that sucks OP.

It was important to me that my ring was built to last because I have a physical job so costume jewelry would't work. I also would have been completely livid if my fiance ever lied to me over something that silly. A healthy relationship shouldn't include petty lies. However, I've seen first hand how some jewelers are and realize what kind of crap men get told regarding rings. I feel like he may have lied because of that. When my fiance and I went to look at rings I fell in love with a diamond one. We sat down and discussed realistic prices for each other's rings and decided to shop for them together so we both loved the rings we would have forever. When we went to look again the jeweler waited until he walked away and was in my ear about how if my fiance "couldn't afford" a nice ring now I could "upgrade" later. Despite me never saying anything about us having a budget or steering away from rings based on cost. I was only trying on rings I specifically liked. I was pissed. I never want to upgrade a ring. It's the meaning that would matter and I wanted to always have the ring I got proposed to with. I later found out that my fiance only wanted to spend a max of $1,000 on my ring (we were talking lower numbers at home so I had no idea he was thinking that much) and was afraid to say that in front of the jeweler because he didn't want the jeweler to think he was cheap. We ended up getting my bridal set, his wedding ring, and all our lifetime warranties for a price we loved and I made sure that rude jeweler didn't get the commission for it.

Stop being a money grabber

Pretend that you pawned the ring for $10,000 and see how he reacts to the news.

They could be just happened to bealike

You should wait until your finger turns green before you jump into any conclusions.

Maybe your fiancé couldn't afford something expensive and was to embarrassed to tell you. Or like others said, maybe the ring he gave you really is special and the one you saw is just a cheap knock-off.

You actually care about the value of a ring who cares if it's $20 or even $5 it could be out of a Cracker Jack box. The fact is this guy is willing to spend the rest of his life with you and you can't put a price on that commitment.

Take it to a jeweler

The lie is what truly cheapened the ring. The value of the ring itself from what OP's fiancé stated was the sentimental value of being welcomed into the family. If OP's fiancé can lie about something this simple with such a huge wave of deceit (the heirloom reference), how can OP trust him after that?