I use a Dymo Turbo 450 http://www.labelwriter.com/
for my businesses it allows me to print address labels and postage from the same printer. Search places like Newegg and you can often find it for much less that what the manufacture sells it for.
On Priority mail, I go direct to the Post Office online site to do my Priority Mail labels as the Post Office will discount Priority mail label costs if you do it on line and you can request the Post Office to pick up the package at no extra cost.
If you need Priority mail boxes, set up an account with the Post Office, order the boxes on line and they will deliver them to your door for free.
Most of my shipping is First Class, small packages under 12oz and Priority Mail. I rarley ship parcel post any more.
My 2 cents worth