There's no good way to estimate it, I'd just go for google ads to start and see what you're getting and graph that out as ALee said. Your best bet would be to

There's no good way to estimate it, I'd just go for google ads to start and see what you're getting and graph that out as ALee said. Your best bet would be to find out how much traffic you're getting each month and attempt to privately sell ads. You can get much higher CPM if you sell private ads versus going through Google.