Jeff – there are no benefits (I assume you are talking about health insurance, etc) if you are an independent contractor, not an employee. If you are a part time employee, you probably don’t qualify for benefits either – you would have to read their employee handbook.
If going the independent contractor route, you should expect to pay state and federal taxes including social security and self employment tax, overhead, insurance, etc out of the hourly wage you are proposing. Generally independent contractors take out 30% for taxes. You will have to fill out a W-9 and recieve a 1099 from each firm at the end of each year.
The benefit to the firms is that they don’t have to pay unemployment insurance, benefits, etc so while your rate would be higher than an employee’s hourly rate, it could end up costing them less money. You are taking on all of the risk yourself. Thats my 2 cents…