If you have a good 30 dollars left over, and if you can get 10 dollars a month, then you should get this game.
Anyway, unless you have a lifetime supply of 10 dollar bills in your wallet, this game is not worth a buy. Paying for 10 dollars a month is just pathetic and a huge waste. A more better price could be 5 dollars a month or 2.50! Online does have a lot, but not much as a full MMORPG has.
The story is pretty good and worth a rentals time, and if you beat a pretty good amount of time playing story, you should try EXTRA mode. It's like a free online without the online part. EXTRA mode and Online mode are basically the same thing. You create your character, and giving a small supply of weak weapons, armour, and some healing items to start. The only thing about online is that some things you have NO IDEA how to do. (Unless you read the instruction manual)
Phantasy Star Universe is a good game, and the DLC is worth more time, and future DLC episodes to come. I recommend renting it first. If you like it, buy it. But BE WARNED! You really need a lifetime supply of 10 dollar bills or it's worth $1.00 on eBay.