This would be super simple. One tier, limited to 100 backers at most. $25 pledge. And with the money you go to paper stores and buy a bunch of different nice notes with envelopes, and each person gets 1 from each different kind.
This would be a fun way to get a sampling a bunch of nice types of notes. Perhaps you could even do it with as few as 10 people, which gives you $250 to buy note sets.
Maybe a spinoff of this could be doing a bulk order of notes printed from photographs, and each person gets to submit a photograph, so you get yours and then also other peoples.
Actually, if it's done through Kickstarter, it can't just be redistributing existing sets (though you could certainly do that off Kickstarter). Either have some artists that will make the cards, or invite the backers themselves to be a part of it.
This could be tiny (as small as 10 people) and still be fun.