You could probably apply for the Amazon accelerate program and get $15K from them pretty easily.
The $15k of credits are only for "startups in select accelerators, incubators, co-working spaces, and other startup organizations".
Hosting companies give away free credits like candy. Don't let the lack of incubator stop you from asking. I've gotten up to $10,000 in hosting credits just by emailing someone and asking for it. No contract or anything, they just added credit to my account.
(BTW, Tarsnap isn't in any incubators/accelerators, but if someone wants to throw a bunch of AWS credits at me I'd be happy to have them!)