Not if, as R2 says, they only charge for objects that exceed a single digit request per second threshold. Your write once read once model still only costs as much as the storage at rest would.
Free per object requests is super game-able. Want 1000 free requests per second, just rotate through 100 identical objects.
1,000 reads per second is 2.6 billion per month. At S3 prices, that wound cost around $1,040.
100x storage is pretty minimal to achieve this. For example:
100x 128KiB = $0.000192/month
100x 10MiB = $0.015/month
100x 1GiB = $1.50/month