Have dollars ready when you arrive for the $25 tourist visa or in euro, what ever is better value at the time. This will last you a month. If you leave after 6 weeks you will be fine. If you leave after 8 to 12 weeks, you may be fined $60 or so. It’s easier to pay the fine than spend days getting another 1 month or 3 month visa extension.
There is a detailed ” How to apply for your Egyptian Visa extension here.