Hello, there,...
First of all congratulations with your engagement to each other.
Second of all: A remark: If gold prices went up worldwide, it won't be any different in Antwerp, that's for sure.
What Antwerp has to offer is a large array of jewelry shops, located around the central station and in the nearby diamond quarters. As Antwerp is (one of) the main diamond trades in the world, you'll have a very likely chance to find a diamond to your taste.
In the shops around the station, you will most likely find rings already set with diamonds or serial products. Many of them also sell diamonds separately.
There are also many designer and handicraft jewelries spread around the city, which can design a ring to match your favorite diamond. Or you can take your favorite Antwerp diamond home and have a custom ring made at home.
As the concentration of diamond shops is high you might go in and out of shops every 10 minutes, whole day long, to see what's on offer, ask the prices, get informed or try a bargain. And find the diamond or the ring that matches you and the love you have for each other the best... It's a very personal story you're making, so there's no guarantee to success, but there definitely is choice a-plenty.
If you come to Antwerp with the intention of buying, prepare yourself, look into cutting styles colors, how you can recognize quality etc... If you come prepared, you'll most certainly make a better deal. And remember,... Don't be too focused on price alone,... Do you really want to be reminded of those few euros you saved on buying that second option ring for the rest of your life?
Good luck!