20 /week = 80 /mo <— Discount Price <— 25% Mark UP
30 /biweekly = 60 /mo . <— Fair Price <— What its actually worth
40 /monthly = 40 / mo <— Overcharge for infrequency <— 25% Mark DOWN
Make it simple for yourself and the customer. Use whatever method you use to calculate the worth of the job and apply a mark up across the board for scheduling frequency. This obviously only works for recurring work once you get the building looking spiffy again after the first clean. Good luck with the bids =)
It’s also important to understand the type of business also plays a factor. Restaurants will require a lot more work than a lawyer office. Personally, I do window cleaning for lawyers and doctors offices in a downtown area. Town size is about 18,000 people. So once a month $40 cleaning is perfect for them. But the small coffee at $25 per cleaning needs to be more often.