As a 1099 consultant, you charge per hour, every single hour worked and traveled. Usually, it is the same hourly rate for work and travel, but some companies lately will try to make you take a cut on the travel rate. You charge door to door (from the minute you leave your home, till you arrive at your hotel or site. You also need to keep a record of the miles you travel, since that will be reimbursed as well. When you are at home, you charge for the time it takes you to do the trip reports and any other administrative stuff (including your timesheets and expense reports to them).
Now, as a W2 contractor, things are different sometimes. Usually it's also an hourly rate which is reduced from the 1099 rate, but the good thing about W2 contracting is, that you get paid straight time for the first 40 hours and then time and a half for every hour after that. 1099 is straight time, no matter how many hours.
The worst type of contract (financially) is W2 salaried, where you are an employee of a vendor such as K-force or RPS. They pay you a salary and bill twice as much per hour to the sponsor. They make the money and you do all the work. Some other types of W2 contracts will tell you it's not hourly, but a daily rate. This is bologny, since it's pretty much a salaried W2 gig.
If you have decided to do contracting, make sure you are getting the money you deserve. Remember, a recruiter will always try to pay you as little as possible, while charging the sponsor up to 100% of what they are paying you, so negotiate. They always low ball contractors, trying to get them for $50 or $60 /hour. Now you know how much they actually make.
Depending on the type of study (Therapeutic area) and your experience, hourly rates will vary between $50 - $100 / hour.
Good luck to you!