how to add a perm shipping method

hello I am trying to make it at checkout where there will be a mandatory shipping method calculated with either of my other two methods. e.g., i have it set up in WC now if under $10 there is a flat rate shipping cost and if over $10 shipping is free, I want to add a shipping cost that will always be calculated in addition to those. Is there a way to to that with your plug in? Thank you.