If you search our forum for information on the home organ market you'll find that these are difficult times for selling organs. Price can be hard to set as there are localities with stronger response. Your best option is to be ready to negotiate. Your customers love of organs, any previous experience they've had with a model or line, and their individual financial resources will dictate the final value of the instrument. (Regrettably many of us who love organs don't have as much to spend on them during this recession.)
If the organ is pristine and working well (do you play and have tested the organ?) I'd suggest $500 US for a listing price. You may have seen Hammonds selling for thousands, but these are select tone generator models. Your elegante was a later generation that featured LSI chip technology and unfortunately while it provided alot of features in a small case, it hasn't proven as enduring mechanically as the old TWG's.
The difficulty in finding (and the price for) replacement parts is part of what drives down the cost of the older instruments. The best resources for selling are Ebay (sales can be limited by the cost of transportation to get the organ to customers at great distances - but some are out there who will gladly pay the cost) and for a local response I would suggest Craigslist.
I hope this proves helpful to you in getting your instrument to someone who will love it as your father did.