Mr. B.
Th sig Kadet would be a decent enough plane, but the PT-60 is an excellent choice as well. Don't overlook the Tower 60 size ABC either. From all I've heard their newer engines are real good for the price.

If you're not going to buy a computer radio, don't bother with six channels. You won't need more than 4 for learning, and are concerned about cost, so buy a real inexpensive 4 channel radio and upgrade to a computer radio when you're able. (A Tower Hobbies or Hitec simple 4 channel can be bought for about $100.)

Do not reduce the trainer to 3 channels for your wife. What makes you think that you can handle four channels, but that she won't? Be careful, she may turn out to be a better flyer than you. [X(]

Good luck,
Dennis-