How much money should I charge as a photographer?

I'm a computer engineering student in university and one of my hobbies is photography. I have a Nikon D5000 with 3 lenses, and a couple cheap lighting equipment that I've been using for a while on my friends and dog (to practice).

Through a referral, another student at my university gave me a call and asked if I could do a photoshoot for his fashion blog start-up. I've played around with the concepts of portraits, but never in a professional setting, but I agreed, offering him a free photoshoot to see if he still wanted to hire me afterwards.

After we first met he lets me know that he is on a tight budget which is why he didn't want to go to other more professional photographers, but I wasn't a professional so I proceeded to give it my best shot (no pun intended).So I take the photos for about 5 hours, with 3 different outfits each (there were two guys) all around campus, using my 50mm, umbrella, reflector, and remote trigger to balance light and shoot at wider apertures for that nice portrait-with-bokeh look. Turns out they love it, and they agreed to hire me, however, I have not thought of what I would charge yet. This IS just a hobby of mine and I love doing it, but it was quite a workout being their personal photographer all over the place, so I'd like to still be paid reasonably.

I guess my question is, take a look at these photos below that I took today:

And tell me what I'm worth, lol

I was thinking an hourly wage of some sort (with a max.limit of 5 hours) would be a pretty good idea
ALSO: Should you have any constructive criticism for my methods, please do share, as I'm always looking for better ways to take photos

One thing I noticed is that you have your subject almost dead-center in every picture. Try a few using the Rule of Thirds http://www.digital-photography-school.com/rule-of-thirds

Before proceeding with this project you need to have Model Releases signed by the models if they are 18 or older or by their parent/legal guardian if they're under 18.
http://asmp.org/tutorials/property-and-model-releases.html

You will also need a Contract specifying how the pictures may be used. Here is one example.
http://www.printablecontracts.com/Photography_Contract.php

Don't sign away your copyright to the pictures unless your client is willing to pay you for it. You might want to use these pictures as examples of your work in the future.

Since there will be more work than just the 5 or so hours of actual shooting you need to allow for that as well. Downloading the pictures, editing them and making a CD for your client and then going over the pictures with your client, choosing the best of the best and then making another CD of those pictures. Who will be responsible for printing? If its you then add that into your charges.

I'd suggest asking for at least $750.00 + any costs you have for providing prints.