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.
Totally fine, I updated the title to be less definitive and more inclusive. If more people want to donate via LiberaPay then it makes sense to use LiberaPay. I only suggested OpenCollective because of the budgeting transparency which is why in part a few OS I know like Qubes (and recently Manjaro and Endeavour) use it.
LiberaPay does not technically require you to make recurring donations, although I can certainly understand why someone might think that given the UX exclusively mentions reoccurring payments. Basically after however long you set the reoccurring amount (say 3 months), you'll get an email that looks like this which requires action on your part to actually renew:
I once let it sit for an extra month by accident w/o consequence. However, they do strongly hint at LiberaPay's purpose being long term, not short term:
Liberapay is designed for long-term stable funding and only supports recurring gifts.
It's worth noting in addition to supporting one off donations, OpenCollective doesn't require intervention every payment cycle for it to go through, but it's not FOSS like LiberaPay is.
Edit: And for what it's worth the money doesn't have to be routers/components if the bottleneck is time constraints; money could just as easily be spent on bountifying things that fall outside the interest of the core team, but should be done, infrastructure so devs aren't paying out of pocket anymore, or modernizing the project landing page, etc.... ultimately whatever is best for the project