A freind of mine raced for a few seasons. Initial costs to purchase a kart and safety gear ran around $5000 (but you can go higher or lower depending on your finances) but maintainence costs were low. He said major material costs were a set of tires each season and the entry fees.
While I haven't delved as deeply into karting as my friend, I do race a few times a year for fun. And it is a lot of fun. Find a local track and just rent a kart for a few laps and you'll be addicted. And because its karting on a track, that's where the entire community revolves around. Hang out long enough and you'll find someone that will take you under your wings and get you started.
You might be able to rent karts or use a friends, but no escaping getting your own safety gear. Don't skimp on safety gear. Helmet, suit, gloves, boots, get the best you can afford.
And behind every good driver is a good pit crew. Its possible to do everything on your own, but having a friend or two help load/unload, wrench, and handle the logistics can making racing less frustrating. While you're on the track battling it out with the car ahead of you, you don't want to be thinking about if somebody is making off with your fuel can.
Best advice really is just to go hang out at the track and talk with people. Make friends and you'll be accepted quickly into the community.
