I recently bought an ammunition safe from ebay. It arrived this morning. I'm really pleased with it and thought I'd pass on the information.
The safe is made from approx 2mm steel and has a double bolt lock with a double bladed key. The door flap tucks behind the rim that surrounds the opening so even if the door pins are cut it won't open.
The safe came with two fixing anchors and cost £35. If you search for ammunition safe on ebay they'll come up. The seller is based in Tenbury Wells.
I have no connection with the guy selling the safes but I think they are well made and good value.