As a consumer surplus estimate for those years, it's too high.

• In the year 2000 internet access itself had 7% global penetration, and 31% penetration in the developed world; your estimate seems to assume that people with no internet access were getting substantial benefits out of Google
• Search use was less intensive at that time, e.g. because of annoying dial-up connections instead of broadband, the absence of mobile internet, lack of content to search for... see these two pages for data on search traffic, which is up close to two orders of magnitude since 2000
• Services like AltaVista were definitely worse, but could still find pages and were improving, so the value contributed is only the difference between the engines
• 5% of income is way too high to be credible for willingness-to-pay: 20% of American households in 2011 weren't willing to pay for internet access, which includes the marginal search quality of Google among many other features, for a lower cost
• Even $1/week might be too much for much of the world's population, and even a nontrivial chunk of the developed world: people who won't pay $10-20/month plus computer costs for internet access itself plausibly wouldn't pay $4/month for marginal Google search quality
• On the plus side better search encouraged the development of more websites and internet businesses with various good effects