Refer Section 100 in Department of Import and Export Control website regarding the blue permit required for import. (http://www.imexport.gov.lk/index.php/en/vehicles-others.html#issuance-of-license)
Refer Section F12/F13 in Sri Lanka Customs Website on the tax concessions for imports by Sri Lankans overseas (which is none btw). http://www.customs.gov.lk/declaration/mvu
Read this thread in autolanka where a guy did some comprehensive research back in 2013. But the tax structure has changed now making it impossible to import even a personally used car.
Hoonigan,
Did you go ahead with you plan to export from Doha? I own a 2009 Kia Sportage and given the current resell value in Doha, I'm considering taking it to SL with me.