starsky--it is hard to say without knowing the company, job title, expectation, etc. But I understand you don't want to advertise that over the internet.

For a Western-educated professional expat with moderate experience who is giving up a good, equivalent position in his/her host country I think the following is a good rule of thumb. Some packages are much greater, and some are significantly less; it just depends both on demand for the position and how much they want you as an individual--just like anywhere else.

25% increase in base salary
Home leave allowance that is equivalent to the airfare for you and your dependents who travel to Doha with you
Private health care for you and dependents
Visa fees for you and dependents
Car allowance that makes the cost of running a vehicle in Doha roughly the equivalent to running one in the UK. It cost more here.
School fees for any dependents and help in locating an appropriate school
Housing that is appropriate to your status in your company and the size of your family. I am more familiar with family situations, and my sense is that an appropriate allowance would be around 15,000-20,000 for very good villa (including utilities). You could always spend more or less depending on your needs. Some jobs come with specific housing included.

Many companies choose to increase a person's salary rather than provide the benefit--i.e. a higher percentage increase in base salary rather than a car allowance or school fees. So you'll have to run the figures.

As you can see the benefits packages can easily be worth more than the base salary.

Bottom line: It comes down to whether or not you believe you will be adequately compensated for your labor and relocation. And this goes for all of the posters here. Some are willing to work for less or more for a variety of reasons unique to them.