Ya see... I've been in this business long enough to know these things.
Lots of things here. First of all... the amount of time it takes a professional cleaner and the time it takes someone with no experience is 2 different things. where a job might take me an hour, it would probably take you 1.5-1.75 hours.
As far as price goes, before a price can be given you will have to tell us where you are at. For example: if you say you are from Iowa.... Iowa is a big state so that doesn't help. Prices vary from Council Bluffs, Ia to Davenport, Ia. We need to know what city you live in.
Also, are you talking about office cleaning only? Or do you want to get deep in the middle of janitorial? For example: some jobs will want you to take care of their hard floor or carpet. But don't let that scare you away... you can sub it out to a professional.