Those vintage FM converters are indeed the cheapest way to get into some FM. E-bay is full of them , and you can find them usually for under $ 50, often times "new" in the box .
Greg
Wards Classic Car Radio Repair Specializing in restoration and sales of Mopar A B E body radios We can restore YOUR radio usually in less than 14 days Visit our NEW website.. http://www.wardsclassiccarradiorepair.com gregward@mchsi.com phone 256-852-0955