I wouldn't let a few tight wads worry you into lowering prices, there are always those who will never appreciate your time and service and you could half the price and still lose them.
Customers circumstances change, ie job loss, some don't like winter cleans and some work out that you just charged £20 for a clean that takes around 20 mins they then apply (stupidly) a theory that you now earn £60 p/h x 8 hrs a day 52 weeks of the year and therefore are ripping them off.
Just continue with what you want to charge ( which is very reasonable - I'd charge more per window ). Over time you will get experience and confidence on pricing and this cones across to customers so as time goes on you seem to get less messers, you can also sniff out/sense a bad customer.
A good rule of thumb for pricing is you get 2 out of 3 quotes - if you get everything you are far to cheap, less than 50% and you are pricing on the top end and in danger of stalling though lack of work.
Darran