Hi Ian, I settled on buying acrylic cases for my kits, online, at acrylicdisplaycases.co.uk ("other acrylic display cases are available").
I don't know if this example will help, but your post struck a chord because amongst other subjects I'm also putting an HP 0/400 in a case sometime in the next few months, along with an SE5a and a truck, but not with folded wings - didn't think I could make the hinge/joint strong enough. I've simply been getting case covers, and screwing them onto wooden bases.
Anyway, this particular site has the facility to dial in measurements for a custom case, and such a case cover (3mm thickness) comes out at £43.20. But I imagine you want some 'clearance', hence a bigger case, and also delivery cost would add a bit more. For what very little it's worth, I did start off wondering about making my own cases, but decided they would never look neat enough around the edges. And these do look nice IMO. But I guess you know your own budget!

Mark