Speaking of salary negotiations, there is something I always wondered about the US: What is the difference in "pure" salary vs additional costs to the empolyer

Speaking of salary negotiations, there is something I always wondered about the US: What is the difference in "pure" salary vs additional costs to the empolyer? Things like 401k contributions and benefits (e.g. dental or health) certainly come with a pricetag. Seeing as I'm doing remote work from another country, I'm not sure how much that actually saves the company. The same goes for simple things as not needing office space / electricity / ... which I provide for myself over here (as I'm working from home). Does anybody have any insight on that?