Once you get everything set up, it isn't so bad. Their initial cost is way more than their upkeep. I have 2 red-eared sliders and they can grow close to 10" or larger. They do live for a while too. They can get kinda stinky too if their tank gets dirty. I usually change their water every couple weeks, in which I also buy new filters (if needed) for the pump and clean it out. It is worth it to splurge for a nice water pump too. Nicer ones clean the water much better are more user-serviceable, last a lot longer, and are quieter.
As far as feeding them, you usually only need to feed red-eared sliders once every 2 days if you use turtle food, which is relatively cheap. Also, they sometimes I'll go to the pet store and get some crickets or even goldfish for them to eat, just as a treat every now and then.
My turtles are actually pretty social, too. Anytime someone walks by, they start swimming over to that side of the tank.
Be sure to get a tall tank because when I first got mine, they routinely would climb out and I'd have to look under beds and such to find them. I really do enjoy having them though.