Here's a couple fairly recent discussions:
Coffee on delivery truck for a week!What are reasonable shipping costs for roasted coffee?From what I've heard, roasters prefer UPS and FedEx because they are ultra organized on their billing, tracking, and pickups. USPS is cheaper and faster for small packages / coast-to-coast shipping, but a pain to deal with from a business angle (e.g., pickups are not as reliable as UPS/FedEx; if something is missed, the roaster must go to the pickup window of the local post office).
The cost of shipping is disproportionately high for small packages like 1 pound of coffee; if you buy 2+ pounds at a time, the cost of shipping only goes up a couple dollars. Many roasters offer a break on shipping from time-to-time or free shipping for minimum orders (e.g., Klatch Coffee offered free shipping for purchases > $50).