Pretty much everything's been answered but as far as union dues, that'll be different depending on your local.
You can find that out by Googling "Teamster Local Package [your town, state]" and doing a little digging around to find which your potential building would fall under.
...Or you could ask someone you know in the building, if that works.
Then just Google the UPS National Contract to find the corresponding supplement, and use the search function on the PDF to find out about union dues.
I'm at two times my hourly rate plus one dollar per month, and that gets me some pretty sweet
ing benefits (that kick in after way too long for newcomers) so I can't really complain about it at all. Plus, union protection is awesome and I'm willing to pay for that perk.