It is also depends on servos. Usually cheaper radios comes with cheaper servos.

4 channels SkySport cost less, but you can "set" only 1 plane with this radio (trim adjustments, etc.). More expensive (computerized) radios have memory for 6 or more planes. Now, what is better - having 6 planes and 6 radios, or 6 planes and 1 radio (plus flight packs)?

6 SkySports @ $200 is $1200.
1 6XAS (with "flight pack included" ) - $230 plus 5 flight packs @ $120 each totals $830...

Not to mention "headache" (kinda) of managing 6 transmitters.

Consider also, that for 3rd or 4th plane 4 channels might be not enough...

Finally, to simplify your life try to add prices of the components for one flight pack if you buy them separately.