I have a NAS that has 18 TB effective storage, 36 TB mirrored. It all gets backed up to a B2 back blaze which is about six dollars per terabyte - but I'm currently only using about 8 TB at the moment so it's only about 50 bucks a month.

So this might be on the higher end of the price range if you're using up all 28 TB uncompressed since that's about $168 per month though...