Depends on your market. If it is all working and in clean, ridable shape, I'd say somewhere between $300- $450 or so. New entry level bikes are in the $600-$700 range, so you need to price it to lure buyers wanting a more modern road bike but looking to save some money over new.

It is a fairly popular size, and you can write your ad copy to emphasize "entry tri-bike" - riding in triathalons is very hip with the weekend warrior/fitness crowd, especially in the major cities.