I agree with what Muppet says, couple of things...
- The 'Sinai coast only' (non-visa) entry, allows you to enter Sharm, go up the coast as far as Taba, and visit St. Katherines monastry. But if you want to visit any National Park (most notably Ras Mohammed National Park for the diving) you need a visa. You can get this on arrival for �10 (sterling, or US$15). Some agencies will facilitate your getting this visa on arrival and charge you �15, I don't think paying any premium is worth it.
Don't change any � to 'EL' (Egyptian Pounds) in the UK. You will be scalped on the exchange rate. You can change an amount of � on arrival if you feel you must at a 'cambio' (bank booth) before you go through immigration, while you get your visa. Be alert, arrivals at Sharm can be a bit of a zoo, the visa/bank staff know you are tired and stressed, count your money slowly.
But you don't really need any EL at this point. If you want to tip the guy for puting your bag on the bus roof, or in the hold (no compulsion) he will be very happy with a �1 coin (or euro1, or US1). Same goes for the guy who brings your bags to your hotel room. There are many ATMs in Naama Bay, including two HSBC branches/ATMs, ATMs are all I use to get cash, the exchange rate is good (I also take say �100 cash, and what ever other various euro and US$ I have lying around 'in case of emergency').
As Muppet says, it's going to be hot in July! And it will be so dry you might not register quite how dehydrating it is. You will need to drink a lot of water (the local mineral water 'Baraka' is good and cheap (about EL2.5, (20p) for a 2 litre bottle)). If I am diving I drink about 5 litres/day in the summer. Basically... er... you want to be passing a near colourless 'stream' when you have a pee.