Answer two questions first:
What are your startup expenses per domain?
What are your monthly expenses per domain?
What would those two average out over two years figure out to be per month?
For myself it runs:
$15 a month for server expenses,
$20 for isp bills spread out over 5 domains.
$3.25 for the domain name,
$40 for pc expenses spread across 5 domains. (costing out
$500 a year in upgrades)
$20 in other intangible expenses (electric, printer supplies, normal system depreciation, etc)
Altogether, I'd say I $run around $35-$40 per domain per month figuring over two years averaged over 5 domains.
To break even:
$3 cpm works out to be about 450 page views a day.
$2 cpm works out to be about 650 page views a day.
Granted thats not including labor or any other overhead (issurance,medical,etc).
I personally figure 1000 page views a day to be a realistic break even point. and 5000 a day to make any money.
Also depends upon the type of site. This one here has averaged around $6 cpm for two years on an average of 2k page views a day (with some 10-15 fold huge spikes when I put out the Quarterly).
Its all going to depend upon the cpm you can pull in.