My guess is a mid-80's Professional, looks very similar to one of mine. Fully chromed seat and chainstays are unusual and would have been custom ordered. My guess is it doesn't have the Merckx logo on the seat stay caps- never seen one with fully chromed stays that did- but they all seem to have come with the chromed slope crown fork. Frames like that right now are indeed in the $500-600 range depending on condition of the chrome and paintwork. Rest of it, hard to say without better pictures.
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