The cost to your average ransomware crew can be rounded down to zero, because it's pretty darn close. They use automated tools running on other peoples computers and utilizing other peoples connectivity. The tools themselves for most RaaS (ransomware as a service) affiliates are also close to zero cost, as they pay the operator a percentage of profits.

The time is a cost, but at scale any individual target is a pretty minor investment since it's 90%+ automated. Also, these aren't folks that are otherwise highly employable. The opportunity cost to them is also usually very low.

The last attacker I got into a conversation with was interesting. Turns out, he was a 16 year old from Atlanta GA using a toolkit as an affiliate. He claimed he made ~100k/year and used the money on cars and girls. I felt like he was inflating that number to brag. His alternative probably would have been McDonalds, and as a minor if he got caught it would've been probation most likely. I told him to come to the blue team, we pay better.