The standard practice is to have one transmitter and any number of models, each with its own receiver and servos installed. You don't need more than one transmitter, but every model needs its own receiver, battery, switch and servo set--known in the hobby trade as a "flight pack" (which may or may not include the other necessities--receiver crystal for the same frequency as your transmitter, and switch harness for recharging the receiver battery and turning on/off). Flight packs go for maybe $120.

I suppose for utmost economy you could swap one receiver between two models, but you need to be sure receiver and battery are securely mounted (with foam rubber protection against airframe vibration) so they don't flop around when you do loops and turns. Flopping around is bad, makes things crash.