My previous reply was just an example, funnily enough I did a full inside and out clean this morning for a regular customer.
It was a terraced town house ( 2x bays plus a 2nd floor dormer ) reg front £10, when inc. the back £25 - less than 30 mins work. Today they had pre booked insides as well. Took a little over an hour for £50 in total.
As you can see I've just charged the same for in as out. There was no drama involved for me in doing the insides with clutter, nets etc. but I can understand how that may not always be the case. I'd say I'm pretty quick and efficient on the insides - spray mist bottle, applicator and squeegee in a boab and micro fibers are all that's needed .
I maybe way off the mark compared to what others may charge and in need of pricing more confidently but it really wouldn't have sat easy on my conscience had I have charged them £100 for an hours work and doubt they would have even accepted it.
If I were looking for an income boost along the lines of what you've mentioned, an extra job a week would sound more achievable and far less hassle compared to booking times etc etc.