best response confirmed by damyou06 (Contributor)
For gen 2 pricing, the first 100K transactions would be charged with Tier 0 pricing (free usage is used up first each month), then the next 100K would be charged under Tier 1. So the calculation would be (100000 - 1000)/1000*4.5 + 100000/1000*3.01 = $746.50

You calculation for S0 is correct and would equal $100 a month. Note that S0 has a lot of limitations around it, such as the number of queries per second that can be made. That said, since you are only 64 transactions every 15 minutes, this isn't an issue.

The Gen 2 pricing is designed for high volume users of the platform and is a really good alternative to the older S1 SKU. In your scenario, using S0 would make more sense, so choose that option.