Farne
Sounds like you have the same "itis" a lot of us fellow hobbyists have - A champagne appetite and a beer pocket book - LOL!!! As your level within this hobby grows, so does your appetite for high quality fish. I do have a suggestion that may work for you as it is one I am trying to currently employ. Buy a nisai or sansai and leave it for a season and then bring it home. If all goes well, you CAN get a return on your investment, even if only on a personal level of enjoyment.
Best of Luck and Happy Koi Hunting
Mike