the story campaign for all the classes are free. the game has some weird paywalls at first, like you only have a couple character slots open, your action bars are limited, you're limited on how many dungeons/space missions you can do per week... as long as they haven't changed it though, subbing for a single month will unlock some pretty basic things permanently and then you can use the credits you gain from being subbed to unlock a bunch of quality of life things, like being able to use speeders (mounts) at a much earlier level.
i have NO idea what the market is like anymore, but one thing i would suggest doing is either using cartel coins or saving up some money for the AH to buy a colored laser. when you buy them it'll unlock for all your characters and they have like, lvl 50 stats regardless of what level you are. so you can use them on a lvl 1 character for a really nice stat boost.