The biggest cost you can't predict is medical. You can get a Hamad card ( ask the employer to pay the QR100 ). But you'll still need to pay per visit.

Some people - say on ships & oil-rigs, just work & save & if that's your plan ( save money to send home ) then you can also look for your end-of service bonus after 12 months.
That 100% saving. All helps I think.