W124 heater problem. Help!

[Hurshi]

This week it got too cold here in Uzbekistan. The temperatures went down as -10 degrees in Celcius. At these temperatures I am having problems heating the interior with this type of weather. My car has a duovalve type heating system. I only get warm (almost like cold) air from the heater. I know exactly that the duovalves are working correctly however it seems like the amount of water passing through the hoses is very small. The engine temperature stays at about 80 degrees. My mechanic once told me that I am missing some electic water pump that circulates the water through the heating system when the heater is on. He also showed where it should be installed. It was nearby the windshield water fluid tank. Does this electric water pump really exist? What type of expenses are we talking about here?
Please help.