Well, July is a 31 day month with one holiday in it; which is normal; we normally have one holiday each month. (9 out of 12 anyways) So 20 * $3.90 (because a partially used book can be reused the next month) still comes out to $78.
Your philosophy of "I use it on the weekends" matches with Calgary Transit's, and its that philosophy I have an issue with. Because like most Calgarians I own a car. So I'm not going to rely on a once per hour Saturday service to go to the store when I can just use my car.
I hate to say it, but for at least 15 years cities like Winnipeg have offered weekly passes.
link I could buy one of these passes on a 5 day work week, use tickets for the 4 day work week. I can also buy a pass the day before the work week; a time when I have a better idea of how many times I'll take transit for that week.
IMHO Calgary Transit dropped the ball when they raised the passes from $60 to $65 to $70. They should have increased the regular fare, and left the passes alone. If fares were $2.50, and ticket $2.25 with passes being $60, I would be taking Transit every day.