Pay is a couple of thousand dirhams a month higher in UAE than Muscat, but you will pay more in the UAE for equivalent accomodation to Muscat. If you are happy to live in an apartment and get employed by Serco, then the company accomodation is good value and rent capped by the government to be no more than 7% a year. Generally most other things are about the same cost wise I think, although Fox and DD can answer that better than me as they have worked in both places.
The upside I see of being with Serco in the UAE versus direct hire in Oman is that we have a pay review every year where we get at least a small increase, whereas in Oman the guys seem to be promised a payrise for years on end before finally getting it.
Just my opinion though. Cheers