If it was me, I wouldn't waste my time with something like a Corbin seat, like you said, the cost is too prohibitive and by the time you have tested it to find out if it's fixed the problem you've already spent all your money.
I would most likely go down the route of having a bespoke seat rebuild on the existing seat (or on a second hand stock spare seat).
It depends where you live, but I would suggest you try to find a good artisan near to you, so you can visit several times during the process in order to make sure it's going the way you want it to go during the build.
Here is an example of what i'm talking about:
MotoStitch - Your Motorcycle Seat Customised
(disclaimer-- I've not used them but I have used similar in my area)