Entropia Universe is free to play and free to pay! Meaning, you can play for free but it might suck! You can pay to play - but it still sucks!
If you do not need good equipment, armor, faps etc. it of course costs you nothing. I have pulled in around 3K USD myself - or very close to +/- but if I withdrawal now, I don't get near as much out. I didn't "overspend" my money. I used them on armor, weapon (a gun, 2 swords, rifel) and ammo/repairs. *shrugs* but a lot of people did it better than that! Also remember that you are paying for the "more-fun" you might get by having a little money (- not including the annoyance from bugs etc. here). IF you decide to deposit it is a very good idea infront to decide HOW much you want to deposit a month. Because it is difficult to stop when first started.
Good luck