Prices vary widely for consultants, so its pays to shop around. It's important to find one with the right skills and qualifications. In general, the highest-priced consultants come from vendors. Most offer consulting services primarily to enable further sales of their products. Unless there is a compelling reason to work directly with a vendor's consultants, you may find a better value elsewhere.
It is important to ask for and check references when using consultants. Also, find colleagues who have used the consultant, and ask about their experience. Ask the consultant about her prior consulting experience. Ideally, you want a consultant who has worked in situations similar to yours. Be sure to meet with the consultant who will be working on your project before you sign the contract. Introduce the person to key members of your project team. Good chemistry between team members and a consultant is important, especially for high-level process consulting.