Good day,
There is no public way to implement vpn feature inside mac os app. To develop this kind of app you 'll need to use hidden api's and third-part frameworks or develop your own libraries, and this option is very expensive and long-term.
I can develop easy to use os x application with nice look-and-feel where user will be able to choose sever location (country, city), protocol type and after click "connect" button it will generate link to configuration file from your server which will download to user's mac. User will have to click install profile and enter his/her username and password.
We can also add some social links to your app and simple greeting and install tutorial maybe
Nice and simple :) More cheeper and I need 1,5 max for it
Tell me if you are interested
Thanks
Best wishes
Maks