Funny you should mention it...
I spent my Saturday this weekend making a case for my pistols.
I used the case from an old electrical drill, bought some foam, stenciled around the bits I wanted in there, cut them out with a Stanley knife, painted it, and it's currently drying.
Assuming you can find a case long enough, you could do the same - cost me £5 for foam, which is a lot cheaper than £30-£200 you can pay for some cases... And it was fun to make
For longer cases, you can buy cheaper ones that aren't designed to carry rifles... Snooker cue cases, golf clubs etc.
It also means you can have the foam cut to house your rifles
exactly... Including attachments like scopes etc. if you like...
When it's dry I can take some photos to show you if you need to know anymore but there are all sorts of guides etc on the forums and on YouTube.
PM me if you have any questions.