If you sell the collection to a record store they will offer you about 20% of what they expect to get for it over time. If you want to sell retail online to get close retail, consider about a half hour of your time for each album to be photographed, listed, packed, shipped. Consider ~$1 for packing materials each, and 10% or more selling/payment fees if you want to use eBay or similar large market.
When I've evaluated collections to buy for purpose of reselling, I try to figure that I can clear $20/hour of my labor and if the collection allows that after expenses I will buy it. Many who inherit or decide to sell overvalue their collections because of their emotional attachments and the waking up process often takes a while. With classical and especially opera, the values are less and trending quickly towards zero. Cheers,
Spencer