That is actually a really nice model. Effectively it is 300 Search for $5 valid for one month. And instantly renew if you exceed $5.

May be Kagi could also consider rolling over unused search for one month. So if you only did 200 searches, the remaining 100 will roll over to next month so you have 400 searches.

The unused searches likely subsidize the people who use the full 300.

At some point this is becoming a really roundabout way to implement 1 search = 1.67 cents

An AWS-style pay-as-you-go plan would indeed be an interesting approach here.

Do you mean that they charge you an additional $5 (so in a 12 month period, exceeding the 300 search limit would result in 13 payments instead of 12), or does the next month’s subscription payment get moved up to the day that you ran out searches, with the number of payments remaining the same?

They update your monthly subscription's bill date to reflect the reup on 300 searches for the date of the 301st search.

So they charge you an additional $5?

For every 300 searches they charge $5.