Free Conus Shipping/w upgrade options

I know, search the board, and I have and I've found some useful posts but nothing that can tell me exactly how to do what I need to do or even if I need to add some 3rd party modules.

I need to know how to set-up free shipping on products over $50 for conus addresses. Right now I have free shipping enable and over $50 and the zone, but it is not right because any purchase over 50 is being given free shipping.

I also need to have the regular shipping options available should a customer want to pay to have their items expedited.

clear instructions would be most helpful. i can't offer money but i can offer a discount to my store, for the real true answers