I got a referral from the real estate company that manages our rental properties. She has a small company and always comes with a crew of 2 or 3. When I interviewed her, I told her what I did not want done (no changing the beds, etc.) Once, the floor in the room where the cat box is was not as clean as I would have liked. I left it the way they had left it and gently showed it to her the next time and stressed the need to thoroughly clean that floor. It has always been spotless since.
As to cost, I pay $75 per visit (every two weeks) for a thorough cleaning of the bathrooms, kitchen and all the floors. They dust every surface (including baseboards -- every time!) and straighten table tops messes. We live in a semi-rural area. A friend in D.C. said she could only pray to be able to pay twice that and get reliable help. That area is very expensive. A one-time cleaning in the D.C. suburbs can cost $300 and up. No idea what a regular semiweekly cleaning would cost. Costs vary widely depending on what area you are in.