First of all, tree work is not an exact science and the bid you receive from one company may vary significantly from the bid you receive from another.  There may be legitimate reasons for this [company size, equipment used, or merely their location] so, as with all forms of manual labor, I would recommend you get more than one estimate for the job. Although I’m usually the cheapest (primarily due to extremely low overhead—everything is paid for), I would rather have a satisfied customer at the end of a job than one who feels they might have gotten a cheaper price elsewhere once the job is completed.
Another thing that’s important to understand about the tree business is that, due to the great variety of work involved, a one-size-fits-all pricing system is simply not possible.  Each job presents its own unique challenges, so I can’t give estimates for any job before I’ve had a chance to see it with my own eyes.  I don’t say this to sound elusive; it’s just that asking how much a tree job will cost is like asking how much a car costs.  There are many factors to consider first:
• What style of car are you looking for?
• What make of car do you want?
• What features must it have?
• Do you prefer new or used?
• Do you want to buy from a dealer or a private seller?
• Etc.
Similarly, there are many aspects of tree work that need to be factored in that must be seen first in order to arrive at an accurate cost.  For example:
• How big, exactly, is the tree or limbs to be worked on?
• What condition are they in?
• What techniques/equipment will need to be used?
• What obstacles are below, around and sometimes in the tree?
• What risk level is involved?
• What other trees, if any, are near the tree to be worked on?
• What is the lay of the land surrounding the tree?
• Etc.
All this and more is necessary to determine the specific—and most importantly, safest—techniques that will be required to complete the job properly, safely and to your satisfaction.

There's an old saying in business:  "You can shear a sheep a hundred times, but you can only skin it once."  I'd rather have a happy sheep return than make a one-time killing.
Estimates are free, though for jobs further away, several may be grouped together to maximize efficiency.