Patreon has the problem that I can't support someone with $0.50 per month because of transaction costs. Almost all patreon tiers start at $5/month and go up from there. There is a very small percentage of things I use the internet for that I am willing to pay $5/month for.

That's the artist's fault, not Patreon. I've sponsored some artists on Patreon at $1/mo.

I don't think it's a transaction cost issue; Patreon charges my credit card once per month (aggregating multiple $1-3/mo charges into a single charge), and I believe they pay the artists once per month too (aggregating hundreds or thousands of contributions).

I wish Patreon had a model where I could say "I want to pay $15/mo for my internet entertainment" and then just drop in whoever I'm into right now and it splits it among them.

So... the flattr model :/

Are those costs imposed by Patreon or by Patreon's bank and/or payment processor?

Patreon requires you to develop a dedicated following and commit to putting out regular content. The Flattr model would allow non regular content creators to be rewarded based on individual pieces of content.

I tend to agree with the comments above that the Flattr model doesn't work, but I think it would certainly be ideal for a lot of people creating content on the side if it did.