As a rule I would agree with you about the bidding on machines sold on eBay, but sometimes the inexplicable happens and two people who don't seem to know anything about typewriters get locked in a bidding war and drive up the price to some ridiculous level. Just the other day I watched with my mouth hanging open in disbelief as someone actually paid over $250 for a run of the mill Royal Arrow. The best part? Others identical to it are available for less than half that price as a Buy It Now. Nutters!

With respect to what you should list your machine for, only you can decide that. As a collector I notice things like the broken/missing keys, and the missing ribbon covers, and think about what it would take to repair or replace those parts. Regardless of its apparent rarity, because of its condition I wouldn't spend more than $80 for such a machine. When it comes to machines that are many hundreds of dollars, I expect them to be in pristine condition, and complete in every way.

My advice would be to keep your listing as is, and if you don't get any interest, lower the price slowly in increments until you do.