Sure, about 7.6% for payroll taxes which is about 30$ on 400 dollars a week to make it 430$ a week vs 500 for the illegal. Let's say another 10$ a week for unemployment insurance which would put that up to 440$. Not to mention that 440$ a week will be deducted from the employer's revenue which will lower their taxable income even further, whereas that 500 a week isn't deducted legally as it is under the table.
Are there some costs I'm missing that must be paid to employers that aren't paid to people working under the table?