Check ebay for skb cases.
There's loads coming back from Afghanistan and being sold on.
Theres one 4.5' long that had bomb/ mine detectors in. Can be had for about 50 quid delivered.
There's even some floating around with uncut foam in.these are about 75.
I've bought a load as they are very good,they are equal to the peli cases!
They retail at over 300quid!