Need clarification on r2 storage's class A operations

I’m confused about how class A operations is counted in R2. It says If a user writes 1,000 objects in R2 for 1 month with an average size of 1 GB, it will consider as 1million req/month.

Suppose, I have 500 objects, and I will perform write operation to the 500 objects in every two hours. The data per write operation for each object will be around 5-10kb. However, the total data at a time for the total objects will not expire more than 5gb/month, as I will set expirations date to them.

I want to know, what will be my monthly cost on R2, if I perform the above operations.