It actually depends on various factors. The expensiveness and cheapness of the expert has both factors from the customer and the expert. Let us see.
#1. Services offered
Some offer substandard and unprofessional services which means that they are going to be cheap at all times. These people are not going to kill all the pests are required and could leave you with the same trouble that you were trying to fight. Other use complicated chemicals, procedural techniques and after-treatment measures to ensure that not even a single pest is left behind. These are expensive to hire.
#2. Size of the area invaded
You could be having pests even on the roofs and compound. If you get a serious expert, he or she can ensure that all these are removed to make you free. You therefore have the guarantee that all the pests are completely removed. This gives you the freedom to have a free compound and a house that you can live happily. Such big areas cost a lot of money because they need to be approached differently and use a lot of chemicals. If the area is small, then expect to be charged very little amount.
#3. Time required
Sometimes you could be forcing things to be done in the timeframe that you see it is convenient to you. Maybe that time, the experts would be needed to strain themselves so that they create a time for you. This is going to be done but with additional charges on your side. Of you ensure that all things are going to be perfectly done, then you need to cough a lot of money at once. This is expensive and sometimes you could be needed to make a deposit before anything is done.