I'll admit I don't know much about fins. What would be a descent reasonable priced set, that i can use on a few different boards and still work well. Bonus points if you know of a good place to buy or if you have a set you wouldn't mind getting rid of. FCS.
PS feel free to give me a bit of a brief rundown.
Cheers

Good quality fins. 5 fin sets are value.
www.sanctumsurf.com.au/fins/
Vast majority of fins from the major fin sellers/companies are made in China despite what they would have you think so they can charge you more for their branding.

Look on ebay there are plenty of people getting copies made in China with same materials (or even same fin without the branding) at $30 - $40 for a thruster set instead of $60 - $150 which is ridiculous. I've found them to be identical, may need a tiny bit of sanding work on the base on some of them but its worth that hassle

Depends on your budget and how hard you are willing to work to get things for a lower price. You can buy directly from China if you are ready to hustle for it (spend some hours). Or just buy from Amazon for a price that most would be willing to pay.

Or Gumtwee or your local boardist. You could even try ****y beach, next to the body boards.