@mnmdesign after looking at your page, you may need to use a Drop Down widget instead of the drop down form element to show/hide the correct form/subscription button. This would allow you to have 3 or 4 different forms which are all hidden on load except maybe the basic one. Then when you click drop down and select a different subscription model, you have to put an interaction with that button to hide all the other forms and only show the appropriate form.
I’m referring to this drop down widget: http://tutorials.webflow.com/adding-a-dropdown-menu
Use it instead of the form drop down element.
Then use this show/hide tutorial to help you learn to show/hide different elements (you can have multiple interactions per a button, so you’d need several click interactions to make sure other forms are hidden)
Or a simpler solution would be to use just tabs with subscription name on the tab, and the specific subscription model/link within each tab section.
Please let me know if you have any other questions on it 
Thank you,
Waldo