In Spain it is essentially 30% of the salary (for standard salaries). Say the minimum is at least like 300€ (and you are not going to start a startup with 1000€ salaries.
Edit: that is: you have to pay the salary and, apart, 30% of that amount to the soc sec.
Depending on where in the US, even half is pushing it in most of Europe. For juniors, probably 20% of the cost of the US is more reasonable - especially in the 'startup land' of the Bay Area for example.
Edit: that is: you have to pay the salary and, apart, 30% of that amount to the soc sec.