Devon,
The Insurance policies/coverage you will need will depend on the location, type of property, and whether or not it will need renovation. If you plan on renovating it prior to renting it out you will need building coverage for the existing structure, builders risk for the additions, Liability for the location and for the work. Depending on who is hiring the contractors, you may need Workers Comp. Check on your Auto Insurance to make sure it will cover the use if you transport tools and materials for the project.
If the property is owned in a corporation or LLC you need to make sure that they are listed.
Generally for a property you hold and rent out, you will need a policies that cover
1. The Property (Building, Contents, Rental Income, Detached Structures, Equipment, etc...).
2. The Liability
For Residential (1-4 family dwellings) a Dwelling/Fire Policy covers both the property & Liability. For Residential 5 or greater units or mixed use property (residential & Retail/Service/Commercial) the policy will be called a Package or Businessowners. Like the Dwelling/Fire that policy covers both Property and Liability. If the Building or Property are not eligible for the above due to condition or other factors you may end up with separate policies for Property and Liability.
If the Property you are purchasing is in a Flood Zone, Wind Zone, Earthquake area, Wildfire area, etc. you may need to purchase separate coverage for those perils.
The pricing of the Insurance varies so much I don't think you can get a general estimate. You will need to talk to an agent or several with an example of the type of property (Residental, Commercial, etc.), rough idea of the location, what the tenants are, etc.
Hope this helps.