you will easily be able to compare prices when you arrive in sharm. Go down to Naarma bay and you will find many operators simply begging to book excursions with you..... and they will be cheaper than the tour comapnies. BUT you need to check very carefully what you get, while a local option maybe cheaper often there is not always such a good package.
However regarding the above excusions, a trip to cairo is a fabulous experience, though by road it is very long way on a cramped bus or with a crazy taxi driver and will take about 4 hours there and 4 hours back. Flying is the best option as it only takes about 45mins, you then take a taxi or bus to the pyramids and finally to the museum.Doing this independantly will probably save you money, but it depends on your confidence to arrange a taxi on your arrival, it is not difficult but do read up before hand on opening hours costs etc so you know exactly what you want and where and when you need to be at each destination. The other risk is that there will/will not be seats on the flights you want. this is the option that may be worth booking before you go.
Local trips are also easy to arrange on arrival, the trip to the moses mountain takes place very early in the monring, i chickened out on this one so i cant tell you if its worth it. The glass bottom boat ride is in my opinion essential if you do not intend to dive or snorkel, but if you intend to dive or snorkel then i guess you will see more in the water. The remaining trips can also be booked locally but take care with things like camel riding and quad biking, there may be no insurance and your own insurance may not cover you for this trip. have fun