I read somewhere the Barga Mongols are related to the Buryats.
Considering the population of Buryats in Buryat Republic to be presently around 250,000
I don't think they are a high percentage of the 200,000 in Hulunbuir. I got a feeling the numbers will be very small possibly less than 10,000.
This site may have some info
http://www.buryat.org/phpwind/index.php