My wife and I got our engagement and wedding rings from Krikawa[1]. The stones on her ring were synthetic, extremely affordable given the size, and visually flawless.

(Not quite as related, but the process was also really easy; we were able to communicate everything over email, get sizing kits mailed to us rather than having to go in person, and they sent us visual mock-ups and procedurally generated 3D videos of what the results would look like, which was helpful because the rings my wife picked out had been temporarily delisted as they found an issue with it that they wanted to fix, so they went ahead and figured it out so they could make them for us without us having to wait for them to appear on the site again).

[1]: https://www.krikawa.com/