Pay cut switching jobs?

Currently, I work in a job that is a combination of salary and commission. (real estate leasing). I worry that even though my take home is pretty decent, when applying to a newer job, they will only look at my base salary. I work in the Boston area, so I'm concerned if I ever moved on to either another state or part of the country I would receive a lower salary for a sales or management type job. Asides from the monster.com websites, what is the best way to negotiate the same if not higher salary for similar jobs that pay in the $25,000-$32,000 range elsewhere. I feel I will have to start back at the entry level range if I work at a different company. Do many people find moving on comes with a pay cut?