$1500 for a studio in what part of town? As an expat, there are only a few areas you want to consider living and they are not cheap (Marina, JBR, JLT, etc). $2k would be more realistic. $700 for car seems very high. Many people pick up a used car like Nissan Tiida or small SUV. Petrol is cheap. $1k for entertainment? Also seems high (ladies drink free anyway at most places) and pilots can use EPC card for discounts.

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As for bring in the girlfriend - that will be difficult if she does not have a job lined up for visa purposes, and failing that, one can do a visa run to Oman every few months. Living together should be ok, just keep it low profile, although there are tons of flatmate ads every day that ignore that rule.