Thought this was already answered in another post.. :-)
Pair of Cheng-Shins for $40 including shipping from JC Whitney. Some people pooh-pooh these tires, but they are a fair tire for the money. Same deal for Kendas, if you can find them.. they are slightly inferior to the Cheng.
Handybikes offers a 'Hindustan' made-in-India tire for the same price.. I'd take the Cheng any day over the crap that comes out of india. At least the taiwanese have some pride in their QC.
ronayersmotorsports.com offers the OEM Michelin for the Motobecane, and the price was very decent.. about $60 for the set, shipped. I inquired, and they said that the item would need to be special ordered, and take a few weeks.
Does that help?