The price is set based on the total number of products made available to feeds (not the total number of products in your store). Variants are free, meaning you can include all the product variants free or charge.
1/ The price is $1 per 1000 standard product-in-feeds per month. Each converted products (products data needs to be translated to a foreign language (LangShop, Langify, Weglot, etc) or price need to be converted into a foreign currency) is counted as 2 standard products.
2/ If only standard products are involved, the minimum amount is $6 per month.

3/ If there are converted products (there is at least one feed using a translated language and/or a converted currency), the minimum amount is $9 per month

Package Standard Products Converted products
Monthly Charge
MF-6K <= 6,000 0 $6 / Month
MF-9K <= 3,000 <= 3,000 $9 / Month
MF-10K 0 5,000 $10 / Month

If your usage drop, you can always downgrade to save cost, but not to lower than the minimum fees (which are $6/month for only-standard-products and $9 otherwise)