The idea of an ARF trainer is a good one. RCKen put together a nice list http://www.rcuniverse.com/forum/m_4537845/tm.htm
Don't spend a lot of time trying to figure out which one is "best" because they are all very similar. Pick the one that fits your budget and has the best looking color scheme in YOUR opinion.

I single these out because they are among the least expensive and you mentioned keeping cost down.
The Hangar 9 Solo Star 40 and Solo Sport 40 sell for 79.99 at www.horizonhobby.com but they do have a 13.50 oversize shipping surcharge.
The Tower Hobbies Trainer 40 sells for 79.99 at www.towerhobbies.com and they do not add an oversize surcharge.

Also, since you mentioned cost and your kit is glow/nitro, I would not suggest an electric trainer. If you get a 40 size glow trainer you can move the engine and electronics to the other plane when you're ready to fly it. Maybe you'll be able to have both planes fully equipped and ready to fly but this approach gives you flexibility.