The Tower Trainer 40 is a good option. The ARF is around $90 and the kit around $50. I learned on one. They are a good trainer and a good value.

The ARF is covered with "shelf paper", don't count on the covering lasting more than a few seasons, but that is a long life for a trainer.

It is slightly underpowered with the OS 40LA that Tower pushes. I had some trouble getting mine off the field unless it was just mowed. It would fly better with a ball bering 40 or 46.