How to estimate number of man days required for firewall deployment projects?

Hey guys,

I work as a PS consultant deploying mostly Fortigate firewalls. In this new gig, the company charges a a daily rate for my PS work. I have done a couple of migrations so far where I migrated PaloAlto and Checkpoint firewalls to Fortigates, we charged the client for 15 man days for each of these projects. About 150 to 200 rules per fw.

Now there is another project coming up where there is a Fortigate to Fortigate migration at Primary DC and about 20 remote sites. The primary DC Fortigate probably has about 200 policies and UTM profiles applied on most of them. The remote sites will connect to DC through SDWAN. There is also project documentation like solution design and as built documents.

Curious to know how other companies decide how many man days to quote for such projects.