Trust me - benefits cost a lot more than $300 a month.
The benefits that I pay for my $35k entry level employee add up to about $14k per year on top of the salary - and about half of that scales linearly with salary.
Benefits include retirement (10% of salary), health insurance (>$300 a month even for an individual if you're providing decent insurance), contributions to social security and medicare, disability insurance, life insurance, unemployment insurance, and a couple of others that I am sure I'm forgetting right now.
While you're obviously correct that you can buy 'benefit packages', the value of the benefits at a company that treats it's workers (even the entry level ones) well is significant. No doubt you can include these costs in consulting fees, but $300 a month it is not.