Geotechnical or Structural engineer for existing property on expanding soil?

Hi, pardon my ignorance...I'm (or I should say was) about to purchase a house in AZ and I highly suspect that it is an area of expanding soil. Should I hire a geotechnical engineer as part of my home inspection before buying the home or is it overkill?

Also is that a service you guys even provide or is it mostly before a construction is built?

Also if that's something you guys occasionally do what kind of $ should I expect for the service?

Happy for any guidance, never dealt with this until realtor pointed out that it's quite common in the area...TIA (sorry for the extra *)