The sport is pretty easy to get into with a fair learning curve aslong as you realize you're combining kiting skills with wakeboarding/surfing/snowboarding, etc ... but the sport is inherently dangerous if you dont take proper precautions - a few people have died ( a lot more suffered broken bones) from improper techniques or carelessness.
Definetly get a trainer kite to start with (2M - 3M, 2 liner). This is just to get your kite control skills down pat before you try to add in the next set of skills - boarding, surfing, buggying .... Learn the basics of wind interaction with your kite. Like any sport, the $$$$ will soon add up as you need different sized kites and boards for different wind conditions along with a good harness, helmet, PFD, impact vest, wet/dry suit if you live in colder climes. Expect to budget about $1500 - 2000. You could go used gear but the newer 2003+ kites are highly improved for performance aswell as safety release systems. Trainer kites are pretty much the same and used would be fine - expect to pay $50+ used to $200 new. Lessons would run you anywhere from $40/hr to $150/session depending on whats covered.
Lessons from a qualified instructor/school would be a highly recommended, especially when you start dealing with the larger kites (8M - 20M!!!). They'll teach you proper techniques for launching, relaunching, landing, self rescue, waterstarting, jumping techniqes, kite to wind selection .... a lot of things that would greatly reduce your learning curve and to avoid preventable harm such as getting dragged down the beach or being lofted and smacked into very hard objects. The kiteline also has the potential to remove body parts when under tension and it's something that you dont want to get tangled with.
I started with a used trainer and took lessons from the local shop. The shop credited the lesson costs towards my kite gear which was a bonus.
Check out
www.kiteforum.com - its one of the popular forums for discussing kite surfing related topics.