The economics of hosting?

I am considering making the move from wordpress.com to a hosted blog. From what I can see, it usually costs around $8 per month if you find a reasonable package. My question is – at what point can hosting be expected to pay for itself?

Very approximately – how many visits per day would I need in order to generate enough money through Adsense (or some equivalent) in order for the blog to sustain itself? I realise this depends upon click through, and the type of content you are hosting, I just wanted a rough idea.

If any of you can share your experiences on this, I’d really appreciate it. I don’t want to make money from my blog, but I’d prefer it to sustain itself.

Apologies if this question is off-topic, or has already been answered – I searched around, but didn’t find any answers.

Thanks,

BB