What should I charge for freelance app development services?

I was approached by someone that wants an incentive/rewards app built in the same style of one of my apps. In fact this person originally asked if they could buy a copy of my source code, but I said that I would rather create a custom solution to protect my own brand.

The buyer is requesting a price for my services but this will be my first freelance job of this nature and I have no idea what to ask for. I will be designing the application (minus graphic design) as well as the server back end for user registration, login, credit tracking, and advertiser postback. What should I charge for development considering I will be able to use my current app and script as a template?

Feedback from freelance app developers and others in the know is greatly appreciated.

The problem is not the price itself, the problem is to explain your price to the buyer. If it looks logical to him, he will accept the terms, or will have a logical base for bargain.

So the math should be simple to understand for him - it will take you x hours to build the app, and you charge y per hour + any additional costs involved.

marco... don't do the job. You will be giving up source code that he can use to cripple whatever business you have now. Its just not smart to me. If the software is your greatest asset that is the focus of the running of your business, why do you want to give up a variant of it to a potential competitor? No man, focus on your business as you have been doing and ignore stuff that falls outside of it. This will just be a distraction that takes you off your game.

I am considering asking for a substantial amount for the task based on both my time in development and the fact that introducing competition into my niche may cut my profits.