Is there an easy and inexpensive way to get a replacement key for my JKU?

yes go to your local lock smith they should be able to make you one and program it for you. I lost my spare and that's what I did. it was like 70 bucks. a whole lot cheeper then the dealer
 
When I recently bought my 16 JKU it only had one key. Is there any easy and inexpensive way to get a second?

As mentioned above, go to a good lock smith who does automotive keys. Do NOT go to a Jeep Dealer.

My daughter lost one of our JK keys a couple weeks ago. My first call was to the dealership where we bought the Jeep. They quoted $125 for the key and $80 to program it, plus tax. They also said I would need to leave it with the Service Dept or sit and wait an hour or two to get it done.

After that I called a locksmith down the road and he laughed when I mentioned what the dealership had quoted. Super nice guy. He did the entire thing for $85 and it took him 5 minutes to program the key. I’m glad I made that second call and he has a customer for life.
 
I paid the dealer almost $200 for a new key when we bought ours because it only had one. 🤦🏻‍♂️ I want a third just in case so I’m going to try a few ideas from this thread