Naturally, we all want to know how much something will cost before we're willing to commit to a purchase. Our office staff typically gets a couple of calls each day asking for "a ballpark estimate" for tree services. The problem is that no two trees are identical and neither are any two job sites. The pricing for tree work depends on several factors.

Location of the work site: Driving time adds cost to any job. Some sites will require access to waste collection facilities.
Specific work to be performed: Trimming a tree is like a haircut, it really depends on how much needs to be removed.
Type of tree: A nice mature Red Oak may be quite a bit larger and heavier but a Monkey Puzzle can cut the climber and crew into bloody ribbons. 
Size of tree: Trees are like people, the tallest ones are not always the largest. The amount of brush, distance the climber must ascend, and the girth of the wood to be handled, all matter in the estimate.
Health of the tree: A dead tree that has been left standing for awhile may be extraordinarily dangerous for a climber. The wood can shatter like glass and without warning. Old dead trees may require some bracing or the use of a bucket truck.
Disposal method of wood and brush: Getting the wood off the property is time consuming and can involve disposal fees. Chipped brush also requires dumping and may take multiple trips away from the job site, depending on the size of the job.
Stump grinding: Stump removal can be done through chemical application or the use of a stump grinder. Grinder time depends on the type of wood, girth of the stump, and the amount of surface roots. Chemical treatments are similarly calculated but don't involve the removal of grindings. 
Drop zone under the tree: Whatever is removed from a tree must be dropped or lowered by rope. Any obstacle that requires special protection or prevents the crew from moving under the tree will increase cost.
Access to equipment from the tree: Cut brush has to be taken to the chipper and wood must be carried to the truck. Distance matters not only for time but for the endurance of the ground crew. In some cases, a small front-end loader can be used if there is sufficient access. 
Likelihood of customer property damage: Fragile items under a tree or nearby windows involve risk and must be part of the estimate.
Weather: We work in all weather but extreme heat and heavy rain will delay job completion.
Requirement for specialized equipment: Cranes, loaders, stump grinders, bucket trucks, chemical applicators, and log trailers may increase cost. In some cases, their judicious use may decrease cost by limiting man-hours. 
Permits required: Most jurisdictions require owners to get a permit before removing certain trees. In some cases, the permit application must be done by the tree service. 
Customer's desired timeline: Odd hours require special scheduling and a lack of notice may require the rescheduling of pending work. 
Electrical lines and water mains: Electricity kills climbers every year. Tree companies must consider potential damage to utilities and danger to employees before beginning any work. 
Current workload: Work that fits into a company's schedule will be less expensive than work which disrupts other commitments. 

Considering the above, no reputable tree service can give an accurate phone quote. The good news is that no reputable tree service will charge a fee for a written estimate. 

There are several things a potential customer can do to lower service costs:

Be responsible to clear the work area from around the tree to the street. If a tree company must transplant your bushes, move your mediation garden, carry your furniture, cover your pool, remove your sprinkler heads, pick up your dog manure, roll up your hose, remove your bird houses, lift your statuary, or remove your fence, the job is going to be more expensive.
Keep the wood. Tell the estimator the amount and piece-size you are willing to keep. Check with friends who need firewood or call local churches and charities who may collect the wood for free. The less wood the tree company must handle and transport, the less you will pay. 
Keep stump grindings for mulch. Grindings are simply a wood and top soil mix, usually suitable for flowerbeds. 
Be flexible in scheduling work. Let the company schedule your job with other work in your area, saving you from bearing the entire travel cost of a truck and crew.
Get your own permit if possible. Estimators want to sell and compete jobs rather than file paperwork for potential jobs.

Be willing to talk candidly with your estimator. If the quoted price is more than you are willing to pay, ask for alternatives. In many cases, customers can reduce the amount of money spent on tree work with a little preparation. 

If you have any questions, advice is always free: 1 (800) CUT-TREE.