Beginner RC

Check out our "GWS Pico Stick for Newbies" at
Randy Model Airplane Engineering

That's kinda a loaded question, since you don't tell us if you want to go electric, IC, size, etc....
The absolutely cheapest plane would probably be one of the SPADS. They come in all flavors from trainer to 3-D, and are mostly geared for glow engines, although you could also electrify them. The spads are not "mini" planes, and will fly with standard servos, receivers, etc. Useful if you are thinking on going on to standard size planes. I personally prefer IC engines, but many prefer electric. Pros and cons for both.
Check out if you think you might be interested in a SPAD. You do have to build them yourself, but they are simple and sturdy. Building your trainer in the first place will go a long way towards understanding it when you need to fix it.
Lots of decent balsa trainers can be found at most hobby outlets. Most trainers are high-wing with a fair bit of dihedral. Some are 3-channel, others 4-channel. I personally learned on a 4-channel plane, although some may say 3-channels is easier for learning. Building your own balsa kit is rewarding. They are fairly sturdy, and can be repaired in all but the worst crashes. I learned on balsa trainers, and went through 2 or 3 kits in fairly short order before whipping the learning curve. If you are in an area with a club, get involved before starting out. You will find lots of help, advice, and most likely an instructor (which will save you planes in the long run).
Knowing what I do now, I think I'd strongly consider a SPAD trainer. They aren't quite as slow as some of the balsa birds, but you can't beat them for cheap and tough.
Bob

Listen to the advice of the people who are already flying. Decide whether you want "wet" or electric. Join a club. Its members will help train you. If you try to fly without a teacher you will crash your first time out. But remember too, if you fly you will eventually crash.
snipped-for-privacy@ssccorp.com wrote:

1) Hogwash. I'm already flying (therefore a member of the class of folks you're supposed to listen to), and never joined a club or had an instructor. Still haven't, and won't. I didn't crash my first time out... in fact, STILL haven't crashed after flying all summer... and neither did my 15 year old son.
2) Rather than an instructor, use a flight sim. You _do_ need to practice, particularly keeping your orientation when flying towards yourself. However, even a simple free flight sim like this one:
will do that for you... and you don't need any silly "dongle" to use it. If your radio has a buddy box port and your computer has an audio in jack, it can probably use that to interface with this sim... and it will run on Macs, too.
3) Fly electric. It's hard to go wrong with a GWS SlowStick. Cheap, easy to assemble, VERY forgiving in the event of crashes, and easily and nearly endlessly modifiable... See the huge number of incredibly long SlowStick threads on RCGroups.com for some of the modifications. (Imagine 6 motors, 4 booms, two doubled wings, doubled tails...)
It's slow (more time to react), extraordinarily maneuverable for a 40" span plane (though very stable and only mildly aerobatic), light (17 oz all up weight is considered the high end for an unmodified version) but very stable in the air and makes (among other things) a very good aerial photography platform.
Three sets of nicad batteries, a charger you can plug into your car, and a few extra props will keep you flying all day.
The only "problem" with the Slow Stick (it's really a problem of patience with the pilot, not the plane...) is that you can't really fly in winds over 5 mph. However, you don't have to go to a big field to fly it, either. I've flown mine in an elementary school half-size basketball court for a RC demo. I can fly it in my front yard... and my house is in the middle of a 1 acre lot, with a lot of big trees. One half of a soccer field is more than enough room... as is a softball field infield. These things are _true_ park fliers.

I'd try the Global Cessna 180. Its a reasonably priced RTF electric thats easy to fly. I started with this plane and had no instructor and learned to fly in just a few weeks. I highly recommend it.