I also charge about $25/mo for hosting with no help or support after the site is live. At which point, it is $80 for them to call/email me and if their needs exceed what I can do in one hour…I quote them for their request/issue.
Otherwise, I package retained time + hosting.
For example: $25/month hosting + $275/month for up to 4 hours of my time (whether they call me and use me or not). Again, any requests they have that would exceed 4 hours, I would quote them separately.
This is all laid out in a contract and they understand the details before signing. This is just rough numbers, depending on the size of the client, size of the budget, size of the site, and my personal relationship with them…sometimes these prices vary, higher and lower.