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If you set the debug on in the admin preferences, then you can see how much and which queries are done for each page generation.
The number depends greatly on the complexity of the site. The number and kind of modules may introduce a lot of queries.
Most important is the number of blocks displayed on each page. Check if each possible block needs to be on each page. find a compromise between useful and need, and plain simplicity.
I don't know the number of pages and visitors or the requests allowed, but you may count on 15 to 20 SQL requests per page.
When hosters start to complain about this, they have mosttimes overloaded their servers (300+ domains) and are only interested in low traffic, static page domains. If your hoster can not accomodate a reasonable amount, then there is nothing left than to move on.