GCS - Cost migrating data to Archive Bucket
Solution 1:
According to the documentation on Cloud Storage Pricing your estimates seem to be correct. Moreover, the amount of data you would like to transfer is quite minimal so the charges would be low as well.
Keep in mind that Archive storage class implies that reads, early writes and deletions would be charged accordingly as shown here, so if you pretend to access that data often or overwrite the files therein it might be better to stay with the Stadard storage class.
Lastly, there is also a pricing calculator to make this kind of estimates that could be found here.