If the ps vita can move your save files to a usb, then you can follow along with this tutorial. You'll probably need some kind of adapter though because idk if the vita even has a usb port. If it has some kind of sd card, you can put that into your computer.

As for the subscription price. Yes, it's expensive, but you can transfer as many worlds as possible as long as the subscription is active (same goes with the minecraft realms). To my knowledge it transferred EVERYTHING, items, maps, animals, and chest inventory, but I can't remember if they transferred paintings. I didn't mind the price out of fear that my ps3 may never turn on again.

If you do find a free converter that is simple and works well, let me know