Pricing personalized software? [closed]

Question

Currently i'm working on a Purchased Order System Application Project for a small scale company.

The Software that i am working on is personalized based on the on their business requirement.

The company told me to create proposal include the price how much is the application is so they can process the check for me.

The person who give me this project is the company supervisor and also a former supply chain supervisor in my employer before which i work also in some of their applications back then.So i want to be fair.

This is my first time to create an application as a sideline so i really never experienced pricing a software even though i am working as full time web developer in a big company.

Any tips and help ?