Used, buy 72. New, buy 2.4. As far as trainer (buddy box) - you can mix and match. If you buy the local setup, it'll buddy with a 6EX 2.4 or a 7CA 2.4 just fine. Or you can get a buddy box real cheap - I'll send you one for the cost of postage.

No way I'd buy a new 72mhz system today. They cost 75% of the cost of a 2.4, and are obsolete. A new 6EX 72 is $180 at Tower, a new 6EX 2.4 is $230. The 7CA is $240/$320. Looks to me like 6-7 channel Futabas won't be produced on 72mhz much longer. IMO, a used 4 channel FM is worth about $50 complete. Check Ebay and see what they are selling for - and see what they sold for a few weeks ago. Used 72 stuff is in freefall.