If you are not into doing MFG homes I would suggest you find someone to work under. Take the AI course, join the Mfg Home Assoc in your state and at the national level, read of Ms. Jo Ann's and Rich's post on this subject here at the forum.
There is more then just an average price for the subject. You have a lot of detail that needs to be filled out.
MFG are not as simple as many would like to think, by just going to a guide and looking up the answers.
Be sure you are dealing with real property and personal property.
MFG are manufactured to all different kinds goodies add to them. Many, Many options that are needed to be considered.
It would likely be a copyright violation to post information from the NADA guide on this forum. The guide can be purchased from NADA. But, the 1004C also allows use of the Marshall & Swift cost handbook.