Having moved around the world with bikes myself, I am going to suggest just what you didn’t want to hear.
Not for any cheapskate reasons, but for purely practical reasons, use a cardboard box:
1) it is lighter
2) baggage handlers will use greater care with a cardboard box (bit of a generalization, but mostly true).
3) you won’t need to find somewhere to store it at the other end (don’t underestimate how much room they take up, particularly if there is some uncertainty about where exactly you might stay).
4) as you rightly point out, there aren’t many boxes suitable for an mtb. I had the B&W bike case, which was good, but huge!
5) you can fit lots of other stuff in the spare corners, using the weight saved wisely.
6) some of the larger boxes exceed airline size regulations and you risk excess charges due to size (and possibly weight)
7) and, yes it is considerably cheaper.
If you insist on buying one, Bike Box Alan is generally regarded as the best allrounder. But, based on the personal experience you are asking for, I wouldn’t buy a hard case again, and definitely wouldn’t consider risking a soft case.