As Mike Jenvey said: how long is a piece of string?
Do you have a headset on the aircraft or do you have to cart around a pair of David Clarks?
How big is the space on your aircraft - a lot of smaller jets won't fit a bag the size of the link above - laptop cases are popular in this event.
Does your company specify anything? I remember toying with the idea of an aluminium case - but my company says they have to be black.
Do you overnight/4 days away/go tech very often? You may have a seperate case for long trips or just have to keep a spare shirt/t-shirt/Underwear and toothbrush if you frequently find yourself stranded.
Depending what is on the aircraft you might find that all you need is your licence, passport and a pair of shades - so you can fit it all in your jacket.
Your folks may get you a bag for a few hundred £££ as a well done present - or personally I have never paid more than £20 - initially on a laptop case and now on a cheap flight case in WH Smith!