To do this thing the best we need as many information as possible about what it has to be loaded on the new Joomla extension (it's good to know about what structure / menu you are thinking about, it's good to know as many of the texts and images before giving the order, it's good to give access to the server to be able to install it and test the extension in the right running conditions). You can't make the order without filling in the phone number or the email address, they are necessary if we need to to clear some things and to deliver the best way the website if the access to the server where to upload the application on is missing).
The price for Joomla extension starts with 100 euros but if it contains too many things and if it requires too much time the price can rise. It should be ready in a few days and the developer will estimate exactly how many days.