It's very hard to have a "one price fits all" model for video. Each project is going to have its own challenges and often what seems like a small detail could have a dramatic effect on how much time it takes to finish.
Determine your hourly rate, you can start low to get some experience at first. Your rate will increase as you get more experience and have more equipment. Sit down with the client and discuss what they want to do. Try not to give them a price on the spot, but go home and then estimate how long it will take you. Send them a quote with itemized task times like "On location shooting - 1.5 hours", "Editing 3 hours" and so on, then multiply the total time by your rate. This helps the client understand what they are paying for, and make sure that you don't end up getting underpaid for your time. Also, that way if they come back and ask you to add things (and they will), you can simply add hours to the project instead of working extra for free.
As a side note, your audio on the demo is really rough. The dialog is only on the left channel and please, please get a microphone that's not on the camera. People will ignore a lot of visual imperfections, but bad audio is something that everyone notices, and this immediately puts your videos into a less professional category.