At the moment the $75 bikes in Walmart are terrible - but mostly because they try and copy $750 bikes with 24gears and full suspension. If you wanted a green solution make very simple, single gear, hub brakes, steel frame bikes in the same factory for $50 and make millions of them.
There is a city bike rental scheme here, but like all the other rental/free bike schemes around the world - it uses some 'novel' bike design which somehow end up costing $1000 each! And so either require credit cards and security or they only distribute 10 of them around the city.