ARF vs RTF cost can be about the same, or very different. If you buy ARF, you choose the engine and radio. You can spend a little or a lot on these items.

When you talk to the instructor you should get some direction from him regarding "what" to buy. Getting something he's comfortable with will be a plus. You'd hate to go with XYZ product and find out the instructor had a bad experience with it and really likes QRS better.

Something else to find out about is channel usage. Our club has 38 members. At least 6 have transmitters on channel 44. Luckily they're never there at the same time; otherwise they'd all be taking turns using the channel. Getting a radio on a fairly open channel will minimize waiting time.

Many of the popular planes have their instruction manuals online. The manuals typically give a detailed list of the tools and equipment you'll need.
Hangar 9 - look at www.horizonhobby.com
Hobbico & Tower Hobbies - www.towerhobbies.com
Global - www.hobbypeople.net