You will need to have an microflow where you pass the current object to that microflow behind the Get Quote button. In the microflow create the parameter with the right object (the same object whith all the fields you are using). Now you can use that object to do all your calculations.
And if you have further questions edit your post and tell us where you get stuck.
I do not think you need any return type. In the onchange microflow just do your calculation store the result (I assume in this same entity) and do a commit and and maybe a refresh if the result field is also in the same form. If the object should only be committed when pressing a button you can even forget the commit action.