There are an amazingly diverse group of providers performing liposuction surgeries. In California, physicians assistants can even do liposuction without a doctor present, just reviewing some charts after surgery. Dostor's of Osteopathy, Dermatologists, Cardiologists, etc. who aren't even surgeons can perform liposcution.
That being said, there are many facilities that lipo can be performed, extremes including in just an examining room to in patient hospitalization. Because of this, each doctor will have his own way of charging, but basically, the more personnel involved and the longer the procedure, the more expensive will be the surgery.
Today, the majority of lipo is performed with Tumescent Anesthesia, where fluid with the anesthetic (Lidocaine), and a blood vessel constrictor (epinephrine) are placed beneath the skin and within the fat to be removed with a small but long needle or cannula. When this is done, no additional anesthesia or sedation may be required, and the surgeon essentially performs the numbing, much like a dentist would, and then also performs the lipo, with no anesthesiologist required. However, many surgeons are not comfortable with this, and opt to have an anesthesiologist manage the patient either with general anesthesia or IV sedation, and this costs more.
The anesthesiologist essentially charges by the hour, usually from the time the patient comes into the room, until the dressings are in place and the patient is awakened. The first hour is usually much more than the additional hours (or portion of hours) because of the set up time, performing an examination of the patient, and coming up with the appropriate anesthesia.
This is a very long answer to your question, but you can see that it may take twice as long to do two areas as it does to do one area, and therefore the anesthesiologist's charge may be twice as much. But realize that in lipo, there are no shortcuts or time savings from using a laser, Vaser, BodyJet, Microaire PAL, etc. and the longer a surgeon takes, the more fat can be removed and the more even the fat removal can be.
For me this translates to using only the Tumescent Anesthesia and not resorting to the use of an anesthesiologist for almost all of my lipo cases, even very large removals. However, in California, only 5000cc of aspirate can be removed without requiring the procedure be performed in an accredited ambulatory surgery center.
I recommend that you find a board certified Plastic Surgeon in your area who is experienced with Tumescent only liposculpture, preferably microlipo who practices at least 50% of his practice on lipo