It’s always better to ask yourself how much budget you can afford. But here we would like to help you to understand how to know the estimated cost to advertise on Google.
As stated above that keywords affect the cost of a Google ads campaign so you can ask the company for the number of keywords you are going to select for your PPC campaign. You can check the CPC on those selected keywords and add the agency pricing they are going to charge to manage your PPC campaign.

For Example: If you have an ad where Max CPC is 25 INR and you wish to get 100 Clicks Per Day then the daily Google Ads budget would be:
25 INR X 100 Clicks= 2500 INR Per Day and 75000 INR per month.