I get a headache just thinking about how much more it costs me to send my son to cram school these days.
It's pretty stressful thinking about how much extra money I have to pay for my son's cram school because he's preparing for his entrance exams for university.
ーI get a headache just thinking about how much more it costs me to send my son to cram school these days.
「最近、息子を塾に通わせるのにあとどのくらいかかるのか考えただけで頭が痛い。」
I get a headache just thinking about ... で「…を考えただけで頭が痛い」と言えます。
cram school で「塾」
ーIt's pretty stressful thinking about how much extra money I have to pay for my son's cram school because he's preparing for his entrance exams for university.
「息子が大学受験生だから、彼の塾にどれだけ余分にお金を払わなければいけないかを考えるとかなりストレスだ。」
It's pretty stressful thinking about ... を使っても表現できるかと思います。
entrance exams for university「大学の入学試験」
prepare for his entrance exams for university「大学入試の準備をする」
ご参考まで！
カナダ 
