How much does it cost?
Answer 1: With a basic glider kit, servos, and a radio, you could probably be flying for as little as $150. Building the kit would involve some gluing, tape, simple cutting and sanding, and could take you as little as a couple hours.
Supplement to Answer 1: It would be difficult to achieve this without the help of an experienced pilot/builder and equipment-tracker-downer.
Answer 2: Because it's so fun and addictive, you will probably end up spending All Your Money™ on it.
What are the gliders made from?
Most of the gliders shown on this site are made of EPP foam, a tough, bounce-able foam that holds up to crashes and retains its shape. This is combined with balsa wood, hardwood, carbon fiber, fiberglass, packing tape, iron-on fabrics...
Is it difficult to learn to fly?
Yes. And no. The initial phase of getting a plane built and set-up properly, and then learning to fly it is quite challenging. You CAN do it on your own, with lots of research and baby steps. It's important to make a good choice of plane for the kind of places you'll be flying. Initial flights can be comical and/or destructive. All this is easier, and you'll be flying faster, if you have someone with experience to help you. With a tough plane and a few hours over a week or two or three, you could learn basic control and be flying. Or not. Depending entirely on... Well, everything.
Where can I fly?
To slope soar, you need wind hitting a steep ridge, hill, or cliff. It takes some experience to learn what makes a good site. You can earn your own experience, or borrow some. For learning to fly, having a friend throw your glider across a large, open field or park works great. But stress the LARGE and OPEN. (Soft helps too.) A football field is probably not big enough, and any tree, trash can, post, puddle or fence will suck your plane into it. A hill works too, but you'll spend lots of your time hiking back up it.
Safety note: Even with a foam glider, it is very important not to fly around people or property while you're learning. Once you are confident with your basic control, it's still important not to hit people or property. Crash your glider instead of damaging something or someone. Don't fly near a road. For a complete list of everything dangerous that could ever happen, consult your grandmother or other worry-wart.
Are you sure you don't need a motor?
Will you teach me to fly?
Yes. Of course. For room, board, and a small monthly stipend, I will come to your location and teach you to fly. If you live close, I'll do it for free.
Most of the gliders shown on this website are also capable of finding thermal lift, spiraling up on a column of rising warm air like a hawk. But -- in my opinion -- it doesn't make a terribly compelling video in most cases.
For a wealth of information about everything R/C, go online to R/C Groups. Hang out in the Airplanes - Sailplanes: Slope area and learn, learn, learn.