Retroactive sales have long been the way most art (and most stuff in general) is funded. Art is made and then sold, then the artist can keep making things. Someone makes them then sells them then they can keep making more. There is also the smaller market of commissioned work, which is popular in illustration and graphic design, but not so much in fine arts as it strips agency from the artist (you are asking them to make a particular thing). Alongside that there is funding applications via arts councils and crowdfunding, the closest for that would be projects on https://mirror.xyz/
Here is a crowdfund for a musician who is releasing records on catalog: https://haleek.mirror.xyz/crowdfunds/0x8B38a9cbabC067ddEA968...
Also as he was mentioned before, here is the crowdfund for the documentary about Stuart Brand too that played with these ideas of free/expensive/public/private https://weareasgods.mirror.xyz/crowdfunds/0x69DdE2e4d81720AE...