Be careful -- I've seen the work of "cheap" installers and they often don't plant the trees correctly, and the trees suffer and sometimes die. Example: I consulted on a job that had been done for someone whose trees were dying -- the installers were claiming it was the owner's fault somehow -- and I could put my arm into the ground up to my elbow, they left so many air pockets. It's worth it to work with reputable and possibly more expensive installers, even if you pay a bit more. Ask around with people who have had this kind of work done and get recommendations. Good installers will also give you a guarantee for most trees and shrubs, usually a year.

Good luck!

If I might chime in here, trees tend to be a long term investment and so you might want to think about future costs in upkeep. The very popular Bradford Pear is relatively inexpensive but is prone to a list of problems as the tree ages. The additional cost of removing a dead or diseased tree can make a "deal" not such a deal. A tree that drops branches or falls on a car or house can really cost some bucks.

Also, the size of the tree you purchase has a big effect on the price. If you're looking for "instant" shade or decor it's going to cost you. If you're willing to take some years for the tree(s) to mature you can find some real bargains from groups like arborday.org. As a bonus, these small starters are usually easy to plant yourself saving you installation money.

Good luck to you.

Now is the time to find cheap trees. Small size is always cheap, so go for a small, quality tree, and plant it yourself. Dig a wide, wide hole. Not as deep as the potted or B&B tree root, so you can plant it higher( by 2 inches or so) than the top of the hole. Add back all the original soil and top dress with 2 inches of compost. Water, water, water.

A few yrs ago, I had to have an installer move a rather large 'skyline' locust. So, I called around and found a guy that had a skidloader with a tree spade attachment. It looks like the sharpened end of a pencil, but huge. First he used the spade to dig the new hole, then used it again to get out the big tree. He even hand shoveled the soil back around the tree, tramping in in well. cost to me was $85.00. total time, about 40 minutes. The tree was shocky and some limbs died off during the next year, but now, 3 yrs later, it is looking full and beautiful. This guy isnt a lanscaper or anything, just a country guy who loves his small equipment. And no, he doesnt go to Chi town. sorry. but, you might find someone like that if you ask around at local nurseries and tree farms.
Pondy