Around 5 of us are thinking of going to Las Vegas during July, is it cheaper to book flights and accommodation yourself or is it better to book a package (flights and accommodation) through a Tour operator ?
I have always found that Tour Operators tend to be cheapest for Las Vegas. If you are willing to go out of season you should be able to pick up a good deal. Try either American Holidays or Tour America for some deals.
I would say book yourself. Myself and another were in Vegas for a week last August and got Aer Lingus flights (transfer in Chicago) for E600 each. We stayed in a couple of different hotels during the week and accomodation cost about E300 each. It wildly varies on where you stay e.g. we stayed two nights in The Quad (directly across from Caesars) and it was E12 a night. That is not a typo. Use alpharooms to check prices and be flexible to get the best deals.
Until you compare you will not be able to see which option makes the most sense.
I was in Vegas in January and we booked it through an agent as they were offering much better rates for both flights and accommodation than if we had booked the flights and hotels separately. We went via London with Virgin Atlantic and stayed at the Encore at Wynn. There was a 300 euro difference between the online prices and the rates that the travel agent was able to secure for us.
We've been several times and always got the best prices for flight + hotel through ebookers. I checked out booking each part separately, and it never really saved me any money.
Have fun!! And be prepared for some serious heat in July!