On first glance appraisal, I'd guess the key is approximately seven to eight buds. But that's only due to the simply fact that I've only seen one other like it, and that was on SOP about five months ago.
For all the people that aren't familiar with this Key, which I'm guessing is almost everyone, since it's not something you being traded often: There were originally 10 Self-Made Nice Keys, given to people who created items inside the s36 Nice Winter Crate. When Nice Keys changed to normal Keys, the Self-Made ones changed too, so now they're Self-Made normal Keys.
Of those 10, there were 2 that got duped (1 once and 1 twice), so there's now 13 Self-Made Keys. And out of those, only 8 don't have 1 or more dupes!
These are my findings judging from official TF2 sites such as the wiki, and the fact that I think I've managed to track them all down (and I found 13 in total). I can't guarantee it's 100% true, but I'm at least very close to the factual amounts :)