Montague has some valid points.
For gas trainers, Alpha, Tower,Hobbico are not bad starters for a 40 sized craft. All should come in at around $300 for a combo setup. I'm not familiar with RC cars but if yours are fuel, some of the field equipment may be useable for planes. However, the only combo substitution I would recommend is going with a 46 engine rather than a 40.
If you stay with planes, the 46 engine will not overpower the trainer but will offer a wider selection for your 2nd. plane. Also, most of the trainers lend themselves to removing the electronics (servos, radio, etc.) to be installed into another plane without wrecking the trainer should you want to return to it.