I hope your ready for a committment. Owning a turlte isn't that easy. It's fun but its not like owning a cat where you basically feed and that's it. A turtle is like a messy fish but simply cooler lol. Turtles can produce a lot of waste that you will constantly need to tend to them. Of course this is when they're young. By 5-6 years old, you will feed them less and they will be fun to have around! (as they are when they are young too, but you have to feed them more)
Basically look at Austin's Turtle Page for care info. I can simply say you'll need two things that are essential. A large tank and a submerssible heater. This heater will be 15-25 dollars... get it so you can submerse it all the way in the water. Have the temperature about 75-80 degrees.
The tank you'll need should at least by a long 20/29 gallon tank. I figure if you can, the bigger the better, so buy a 55 gallon if you can afford it.
A filter is necessary and so is other stuff but those are the first 2 you'll need right off the bat. Get him to eat turtle food or others.. just look on the caresheet for everything you need.