Here is a website that I have had bookmarked for quite some time: http://www.freetreesandplants.com/index.html
I have never ordered from them, but I have "friends" (internet ones not IRL) who have and say the site is legit. They just never have what I want at the time.
Anyway, if you are considering putting in any trees or shrubs in the spring - you really should check it out. You just pay for shipping and handling for the plants ($7.95 per unit I believe) and they provide work for disabled people and keep unsold nursery stock from going to waste.
If you do order - look at the unit carefully. I had one friend who ordered a maple tree (which she loves) and was surprised when it came that it was two trees (I think for most of the trees and shrubs, they all come in pairs - not sure about the other plants) and she didn't have room on her small suburban lot for two trees. She posted on freecycle (http://www.freecycle.org/) and found a home for the other tree. Maybe a friend or neighbor will split the shipping cost with you and each get a tree.
Anyway - since it is the time of year for planning and dreaming of the spring - I just thought I would throw this affordable alternative out there. Anyone who has priced trees at a nursery knows that they can get expensive very quickly.