My early understanding of the etiquette was that if the bride broke it off, she had to return the ring. If he broke it off, or did something really bad, she could keep the ring.
Me, we'd been living in sin for six years, bought our first house, got married in the living room and our son was the ring-bearer. Nice diamond in a classic solitaire setting. Bought it from a pawn shop jeweller for $700. Blanche has always loved it.
I don't know about tax in your countries but thats a hugely good idea here. 'Second hand' jewellery here doesn't attract so much tax so when you buy you get more or less what you pay for. Plus a lot of the older settings are very attractive more so sometimes than some of the new ones. You get more choice in the type and colour of gold you want as well.Same with the way diamonds are cut, theres some lovely Victorian cuts they don't bother with now for the mass market.
( my mum was a jeweller so a bits rubbed off lol)