Not true:
Jet2 Baggage - £19.98 return
Monarch Scheduled - £15.98 return
easyjet - £15.00 return
There's a difference though; Jet2 gives you 22kg allowance. Easyjet and Monarch 20kg. If your bag is 22kg with Easyjet or Monarch the excess baggage charge besides the already bag charge will be much higher than £19.98.