Good info above and I would like to add some wisdom for the newbies who may be viewing this thread:
I personally recommend that a player go with a subscription before they start thinking about grinding in-game currency to buy gametime in-game.
This will allow a player focus on the game itself… its mechanics, intricacies, and nature… rather than grind and/or obsessively look for ways to make in-game money.
Once you have got a handle on the game itself and/or established yourself as an entity that can earn in-game currency and keep it, you can then start thinking about buying gametime from other players with deeper real-life wallets (because that is what PLEX is… one player paying for the subscription of another player in exchange for in-game currency).
Mind you, there are those out there who may balk at ~$15 a month for a game (or effectively ~10 /mo if one purchases a yearlong subscription up front)… but consider the following:
A bottle of so-so wine or a 6-pack of beer costs about $10 to $15 a purchase. And if you are like me, it won’t last a week.
A so-so dinner at a restaurant costs about $10 to $20… and it will only go last for an hour or two.
A night out with friends at the bars will easily cost $20 to $100 a night… and only last a few hours followed by the potential for a hangover and/or a doctor’s visit (for one reason or another) the morning after.
A gym membership can range anywhere from $20 to $100 a month and, realistically, you probably won’t go to it more than 2 to 4 nights of the week for an hour or two at a time.
You have probably spent much more than $15 on a whimsical purchase that serves no actual purpose other than “I want it!”
For between $0.33 to $0.50 a day you gain access to a vast persistent-world MMO with between 10,000 to 30,000 players (at any given time) 23 hours a day, 7 days a week.