I am in Birmingham and I charge a lot more than that, so I think you are too cheap.
The best way to find the right acceptable price to quote at is by trial and error when you first start out.
What you need to do is start at a high figure, then work you way down slowly.
So for the next 10 enquiries you get, quote high and watch their reactions, if they look shocked or refuse your price. then drop your price on the next one who enquires, you kept on doing this, until they go ok when can you clean them., you have now reach the acceptable level that area is willing to pay.
Also point out that the 1st clean, is always double the price, and any clean over 3 months is classed as a 1st clean.
If they question you on this, explain that you do a complete clean, and this takes longer on 1st cleans or propertys that have not been cleaned for sometime, the customers understand this and I never get objections to my prices.
Also never be afraid to quote high, sell yourself and your service and what you are going to do for them, treat them special, it does work, also if you are confident that you are offering a service that is value for money then they will be convinced as well, if you are not convinced, then they will pick up on this and they won't be as well.