The most important factor when you search for a consultant that would be the best fit for you should not be the price but complexity of services offered and willingness to personalize the services. Some professionals charge minimal fees, some charge even double or more.
You should always ask what is included in the fee: Are updates to the application included? Are postal or courier services included? Is the counsel available when you need him? Will he be available once the application has been submitted? Will he be available once you land?
The fact that you hire somebody to prepare your application will not guarantee faster processing or preferential treatment at the processing level. It will help you to get through the process without unnecessary delays and mistakes and to have an advocate if something goes wrong with your application.