I fancied getting a Bofors anti-aircraft gun, for my fledgling 28mm British Civil War force - early models were available from 1937, so it was "in period", and a 40mm gun that could fire up to 120 rounds a minute would be a handy weapon in 1938, when many aircraft were still slow moving biplanes, and even many tanks were lightly armoured.
Only trouble was, to my knowledge no wargames company makes one currently that is suitable for 28mm figures (you can get one in 1/72nd or 1/35th, but i'd ideally need one in 1/56th) - I did find a diecast one in 1/48th, but it was £40, so I decided to have a go at making one myself.
The gun is made from stiff wire, with milliput and plasti card to give the approximate shape of the weapon & mount - I'm not interested in an exact replica, I just wanted something that would like one for the purposes of a wargame.
The wheels were a problem - I didn't have a ready source of suitable resin/metal wheels, so I ended up making them from milliput, and then having to carve/file them to shape - not ideal, but again, good enough for my purposes.
The finished model! Total cost - zero - as all the materials were already in my bits box. I made some extra copies of the actual gun, which may come in handy later on.