Cheaper Ghost hosting
Ghost(Pro) is the Ghost-owned host and probably the best host out there.
But for anyone looking for more affordable hosting, here are a few options.
Midnight
$20/month (Plus plan)
10k newsletter emails
300k page views
50GB storage
Unlimited members
Unlimited staff users
CDN
Gloat
$189/year ($15.75/month)
20k newsletter emails
Unlimited page views
Unlimited storage
Unlimited members
Unlimited staff users
No CDN
Digital Press
$12.90/month (Starter plan)
Newsletter emails not included (use your own Mailgun account)
Unlimited page views
15GB storage
Unlimited members
Unlimited staff users
No CDN
Bonus: self-host on Digital Ocean
The cheapest way to host a Ghost blog is to self-host (what is self-hosting?). This can be as cheap as $5/month.
However, this will require you to do server work in return for a more flexible configuration and complete control of your server.
Digital Ocean is a server provider and they offer one-click Ghost installations.