Currently according to the website
Each of the Hetzner servers costs about 50 Euros per month, for a total of 150 Euros/month.
There is a small annual charge (20-40 Euros) for registering the domain names, etc.
As of late 2016, two core team members are personally covering the costs of the Hetzner servers while another core team member picks up the other fees. So far, no one has stepped up to fund the new servers that will be required in the coming months.
Other private parties generously donate their time & compute cycles, you know who you are and we thank you.
There is a private discussion about possibilities of some sort of crowdfunding to allow the community to pay back the core team for their expenses, and fund the project going forward, but there is no public news yet.
I would like to suggest that the team consider using either LiberaPay or OpenCollective. As much as I love LiberaPay, using OpenCollective would likely inspire more people to donate and generally have less friction as the spending is transparent. Please consider doing this sooner than later; I strongly believe the routers/components OpenWrt supports could be expanded a great deal if OpenWrt allowed people like myself to do things like automatic reoccurring donations.