I have done a lot of research and pondering on these issues myself...
ebcalc.com>>> very easy and free
auctiva.com >>> well worth the time to learn how to use it. After a couple of hours of use, I could never go back to the standard ebay listings. I just played around on the site for awhile and got the hang of it rather easily (I have ZERO patcience by the way).
Although, they do have an education tab to walk you through most features.
BOX ISSUE: While USPS will send you free boxes, you have to wait for them, and you have to use them for PRIORITY shipping which is not always the best way to go. CALL YOUR LOCAL GROCERY STORES, LIQUOR STORES, DOLLAR STORE... you get the point. Find out when they have their truck days, and tell them you are always in need of boxes. Make sure to ask the best TIME to pick them up. It may take a few calls but you will get FREE boxes and SAVE alot of MONEY!