Hi - I think looking through craigslist and contacting property management companies or even just looking on their websites for current rentals are both really good starts - the rental market can change in six months but again should give you a good idea of what rents are in the area. There isn't one centralized place to look for this information but craigslist tends to have the most information in one place.
You asked how an appraiser would estimate market rents - typically they will contact both owner/landlords and property management companies and will do a "rental survey" to get a sense of what a particular property type will rent for in a neighborhood. They place most of their weight on recently rented properties because until something is actually rented - just a rental listing is of limited value.
It is better to think of the potential rent as a range and not as a fixed number - some of the things that create variability in the rent is if the landlord pays for some or all utilities, if the tenant is expected to yard maintenance or if the landlord contracts that out. Rent for the same type of house might vary by over $100 a month if the tenant is paying all utilities and responsible for taking care of the yard over one where that is included in the rent.
I think West Sacramento can be a very good investment neighborhood especially since much of the city is in close proximity to Downtown Sacramento.... more