As someone mentioned up-thread, there are built models for sale on Ebay all the time.
Rather than straight up throwing them out, I would set a low starting point for an auction, and let the market dictate the price.
You would probably be able to generate enough revenue to make it worth your while, in the sense that you'd be able to pay for a new kit or 2 with the proceeds, supplies, etc.
I sold a MG gundam from Bandai, completely built, on Ebay. Only built kit I have ever tried to sell.
I was surprised. I think it sold for something like $80 US. I had completely lost interest in it and didn't want to display it. Selling it sent it to an appreciating home and helped fund something more in my interest range these days.
A win-win for both parties.
If something fails to sell after 2 or 3 auctions (no one bids), chuck it!
LOL