free shipping

Hi Dear CrouchingBruin

I have a problem for calculate shipping cost in my website.
if you can help me again please…

I have two type of conditional shipping that names are:
1- special shipping
2- express shipping

and one of these two types of shipping select by user in checkout level.

this subject works correct on my site but i want to add free shipping for both of this type of shipping for example:
1- if you buy above 50$ in “special shipping” type -> shipping payement is free
2- if you buy above 100$ in “express shipping” type -> shipping payement is free

and i want to display “free shipping” when the total price is above 50$ in first shipping method and 100$ in second method.

please help me again.
Thank you veryyy much