Breaking the radio silence with a nugget found on the interwebs:
The Viennese website on Mari language now makes a whole textbook of Meadow Mari available for free download! It is an English translation of a Russian textbook “Marijskij jazyk dlia vsiex”, but a) it is expanded [esp. the grammar notes] and b) it comes with AUDIO!
All the Ugrofinists among you – including those still in the closet or in denial – should check it right now.