Stuff like that usually in billions
Would be very expensive but I think cheaper per mission, if you start off with a plan to send a lot of them.
Might take in full some tens or hundreds of billions. YC I am aware will not fund on that level haha, but maybe they would have an eye for wanting to start it off.
Here's a cool video describing solar sails that are supposed to be able to accelerate up to a final velocity of 22 AU/year, which get things to 550AU in 25 years.
https://www.youtube.com/watch?v=NQFqDKRAROI&t=883s
This video was based on the paper: https://arxiv.org/abs/1802.08421