I'm curious as to why you would need a structural engineer to examine your purchase so unless you are considering an addition to the existing property I would re-visit your reason for purchasing such a property in this buyers market. Also, I would make sure that whoever you hire has done the type of work your are requesting they investigate. In other words make sure you're not paying for his learning curve. Some people say they are "familiar" with a certain problem but have never actually done the corrective work so make sure you get at least 3 opinions before deciding who will be doing the work, it might cost more for the bids but it would be well worth it in the long run.
The cost for an inspection will depend on the scope of work and the cost of living in your market. Definitely try to find a licensed engineer with more than 5 years of experience (engineers know nothing coming out of college) and with experience with residential remodels and ideally historic architecture. The reason is that a lot of factors may come into play, including the method of construction and construction materials at the time the home was built. Residential structural is actually more complicated than light commercial in most cases, and this type of inspection requires even deeper knowledge than design.