I was looking up on eBay for both cameras. Seems that the FX3 Camera is the more recent one that was released back in 2021 and the A7S III was back in 2020. That also will have to depend on your budget and how much you are willing to spend on it.
Here are the links to both search results so you can compare prices on eBay to see which one works best for you:
Sony FX30 Camera: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=Sony+FX3+Camera&_sacat=0
Sony A7S III Body: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1311&_nkw=sony+a7s+iii&_sacat=0
Best of luck! If I was talking budget, I would go with the Alpha A7S III but if you want better specs, I believe the FX3 Camera can be a more viable option. 🙂 Hope it helps!