$10 per month is really low.
I remember when Contributor was in an internal beta (back then I worked at Google). Initially there were no tiers. I recall being completely shocked at how high my 'budget' had to be to stop seeing just most ads, not even all of them. It was much, much higher than $10 per month.
When I looked at the per-site breakdown it was obvious why: I spent a lot of time on sites that advertisers were willing to pay a lot to be on, like (oddly enough) Slashdot. Presumably due to the affluent, IT-budget-controlling and very tightly defined audience. My eyeballs were literally worth a lot of money and to buy them back, would therefore cost a lot of money.
It was when I started to see those figures, and I wasn't even getting an ad free web, that I realised the whole dream of using micropayments to clear the web of advertising was a non starter. Hardly anyone is going to be willing to double or triple the price of their internet subscription just to get rid of some ads, some of the time. We really have no idea just how much the web economy relies on advertising to survive.
Presumably Contributor uses tiered budgets to avoid sticker-shock and people blowing through their budget in the first few days of the month. It makes sense but they can never get rid of all ads that way.
P.S. I don't use ad blockers.