Depending on which area you decide to live in in Egypt, the safety concerns and level of danger will be different. It is recommended to avoid the North Sinai area completely as there is a high risk of terrorism and kidnapping, and while there is less risk in the Central and South Sinai areas, these are nevertheless dangerous areas. For more, please see the Expat Arrivals guide to Safety in Egypt.
As for the cost of living, this differs from person to person. Our page on Cost of Living in Egypt can give you a rough guide to the cost of various things, and you can also use sites like Numbeo and Expatistan for research.