I have seen the terms 'air bags' or 'air springs' used for the same item. Unless you meant airbags as versus 'helper springs'. Helper springs are different, they are extra overload leaf springs.
The good thing I think about the airbags, is they can be filled with more air to compensate for heavier loads, and then reduced in pressure to resume soft regular city driving while not towing.
Packages vary, but you will find airbags, or helper springs for that matter, for a couple hundred bucks depending on model of spring and vehicle type.
I see similar prices often, but i just installed my airbags that i bought from Summit Racing for what I thought was a good price.
F350 PSD 4x4 SRW, BanksBrake, FOX res shocks, MagHytec, DP tuner, JohnWood tranny;
'63 hog; ChrisCraft Launch VP8.1 ;
3 hound dogs