See the UCSC docs https://genome.ucsc.edu/goldenpath/help/hgTrackHubHelp.html#Hosting
One free option, at reduced speed, is Cyverse. Two other free options, with higher speed but limited file sizes, are Figshare and Github.
As for the paid options, the UCSC page says this:
In general, commercial online cloud backup providers that charge a flat rate, like Dropbox, iCloud, Google Drive, Box.com, Microsoft OneDrive, Tencent Weiyun, Yandex.Disk, etc. do not work reliably as their business model requires rare and rate-limited data access, which is too slow or too limited for genome annotation display. However, commercial cloud storage offers that charge per GB transferred, like Amazon S3, Microsoft Azure Storage, Google Cloud Storage, Backblaze, Alibaba Object Store, etc. typically do work. For optimal performance, select a San Francisco / San Jose data center for the main UCSC site genome.ucsc.edu, a Frankfurt/Germany data center for genome-euro.ucsc.edu and a Tokyo data center for genome-asia.ucsc.edu.
Also, you can send email to the public mailing list at UCSC and ask us, as you did here.