I crunched the numbers in another comment.

Supposedly $5 for 300 searches a month is enough for most people - they claim on average people use Google 3-4 times per day, or 90-120 times per month. However, when you phrase that as 10 searches per day you can easily imagine that you might go over your 300 per month every now and then.
Additional searches are 1.5c each, or $4.50 for 300 searches.
$10 gets you 1,000 searches per month. 1c per search if you use them all.
$25 per month is unlimited, but you get 15% discount if you pay a year up front - $255.
You would need to make 1,833 searches a day with the $10 per month plan for the $255 annual plan to be worth considering.

I agree that it's too expensive. The fact that their individual search rate is cheaper than the lowest tier monthly search annoys me. Then, the only way to get less than 1c per search is to make more than 21,000 searches a year on the most expensive plan.

If I could share my account across a family or a small business, that might make sense, but otherwise it's asking a lot for only a small improvement over the competition.