Create app cost - remove if do not belong

I am developing an app while learning Knack.  What is the average cost for a full app to be developed?

I was asked by a friend to create an app using Knack.  I informed them that I do not know how to use the interface.  However, I have programming and database development experience.  

I have created most of what they are looking for. I am looking for feedback.  

Email me at

Thank you in advance and I appreciate your help.