I think you would have to consider their condition, whether or not the set is complete, how much they cost new, etc. It's hard to nail down a price. Your best bet might be to price them at what they are/were worth to you, and see if they are worth that amount to anyone else. Anyone interested could DM you for questions (or maybe ask in this thread) and negotiations.
Which brings up another question. Do you want to sell them here, or are you putting them online, ie, ebay, FB, etc?