this is what you need to do
1) provide a scope of work on what needs to be done. Never let the contractor decide the scope of work UNLESS they are referred by an investor and do that kind of thing often. If you don't know what needs to be done, then I would suggest finding somebody that you trust that could help. If you don't know anybody, then hire a property management company and they will be able to tell you what does and does not need to be done to get the place rented.
2) once you have the scope of work, get a few referrals for investor friendly contractors and walk the house with them with the scope of work you created. Any good contractor should be able to give you a ballpark price on the spot. There's will always be unknowns, but you should roughly be close especially on a rental rehab. Depending on what needs to happen will depend on if you can just get a sub or handyman to do it all or if you need a gc.