Calculating the sailing time of cross ocean course

[Reuven]

Hi everybody,
I'm somebody with 0 sailing experience, and am trying to organise a long cross-ocean sail circumventing Antarctica (yea, really lol).
My question is: How to calculate the sailing time? While I see data on a ship's maximum sailing speed, I am aware that the speed depends on winds and currents.
tldr; Given the distances, boat type and season, how do I reach the most accurate estimation of the time it will take to travel? And what is the fastest boat that is capable of making cross-ocean travels on a budget of 100k-200k$?
Thanks in advance!