We have used both Merry Maids and Molly Maids for a few years. They are based in Calvert, but their crew service homes throughout the tri-county area. The price will depend on the specifics of your house. They will do w walk-through with you to go over what you want done and give the estimate based on that. If a company doesn't do that, prepare to be disappointed.
We have several rooms that we did not have them clean because of limited use. Overall square footage they cleaned for us was about 2,200, and the price ranged from 100-110 every two weeks.
The issue we had with both of these companies and reason we don't have a cleaning company now is their quality of service declines over time. You'd think it was because the crew was becoming complacent, but their turn-over is so high we would often have at least one new person on the crew every month or so, which is another thing we didn't like. The final straw for Merry Maids was after they finished cleaning my house I found 22 places where they had missed something - things they said they had cleaned on their list. molly Maids was a better experience overall, but they too began to slide after a while.
I guess it depends on your expectations, and perhaps ours were too high. We have 2 long-haired dogs and a cat, so we have to vacuum every 3-4 days. Having the cleaning service vacuum is nice, but not a big deal to us. We were more interested in the full cleaning of the bathrooms, dusting, etc. They all use these lists where they say they focus on "deep cleaning" certain items each visit, but it doesn't always work out that way. I guess it's too hard for them to look around and just clean what actually needs it. For us the hassle made it not worth the expense. YMMV