I got a taxi from central Abu Dhabi to Dubai Marina a couple of days ago & the fare was 185 AED which I rounded to 200 AED & it took an hour and a quarter or so. The airport at Abu Dhabi is closer to Dubai than the city centre. Depending on where you are staying in Dubai could add quite a bit to the fare of course (the Creek for example ia quite a way the wrong way!) You may want to look at a hotel car service if wanting a bit of luxury. These run at c 325 & up (AED) again depending on establishment & location.