CPM rates

Hi
I have been checking around various companies and I am not sure to make of the information I am being given.
1. CPM rates differ from like 0.4$ per 1000 impressions up to 20$ per 1000. Am i reading something wrong or do different companies actually operate with such huge gaps.
2. Do ad networks offering CPM allow publishers to have more than one banner on each page? Do you get paid less per banner if you have 2 or 3 on each page compared to just having one?
3. If I were to put 3 banners on each page of my real estate / investing website, what could I expect to earn?
4. How much could I expect to earn for pop ups? pop unders? (estimates would be greatly appreciated)
5. Does the cpa adnetworks allow you to advertise and bring in traffic from google adwords or similar pay per click companies?
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Original post by sitenewbie99