Total price i have to pay if i want to buy up additionally monthly respondent up to 2,5k respondent in plus plan

I would like to ask regarding the pricing limit if I buy a plus plan and I want to buy up additional monthly responses up to 2,500 total respondents. How much is the total price I have to pay monthly? Since there’s just information regarding the plus plan which is about 59 USD per month and i have been looking for information about the price’s limit i have to bill as my charge but i couldn't get it

Thank you
Your sincerely
Rana Laily