I had to take a summer course going into grade 12, and my parents had planned a trip that co-in sided with the official Toronto district school board summer school, so they gave me a chance to do some research to find alternatives. There are several places in Toronto that are not sanctioned by the TDSB however the credits you receive from them are fully legal to be used in high school. And so I chose the month I wanted to go and it turned out to be cheaper than the official Toronto district school board summer school.
Do so research, look for alternative summer courses that offer the credit that are more flexible to your schedule. Not sure where you are located, but it's worth a shot.