As all things in life, there are plus and minus things to consider.
The nice thing about a bag is that now your poles are in the same place too and you have someting for a quick grab & carry.
A cheap bag ... flimsy, but will offer some protection and it will be small enough to fold and stuff in your other (boot bag??).
Some bags have a bit of padding in the binding area where it's needed, I've seen a few but don't remember the brand. Probably the best option if you can find one and still small enough to stash in your boot bag.
A more expensive padded bag ... yeah good, but now where do you stow it once you hit the lodge.
A tube ... now you have to unload the tube and leave it at the bus and haul the skis and poles.
If these are adult trips ... not like the high school trips where the stuff really get tossed in, you will probably be fine with a cheap bag.
BTW ... I highly recommend the Transpack for boots, it is backpack style and has lots of room for helmet, shell, gloves, extra gloves and goodies .... a good backpack style boot bag is worth it's weight in gold in getting all of this stuff where it has to go while you are dragging skis.