Lockable tool box

Any suggestions for a lockable tool box that will attach to the pannier frame on the non exhaust side without costing a fortune? I've seen a few but they are either for the 1200/1250 or far too expensive. The 800 has plenty space at the rear but the fuel tank cuts in a lot at the front of the pannier frame.

I know there is a tool tube but wondering if there is a rectangular version.

Must be a cheap metal/strong box the right size.

Gone for a tool tube for now, Amazon sell one with a diameter of 110ml which is a decent size, you can "lock" with a grub screw

https://www.amazon.co.uk/dp/B07V3JX1DB/ref=pe_27063361_485629781_TE_item

Still might buy a metal box if I find one but this will hold a puncture aerosol at least