Trade in values are notoriously low for all cars and dealers. You do save on some sales tax by trading in, but I've always found private party is the way to go. I received multiple trade in quotes for my previous vehicle around 13k and sold it myself for more than double that. It takes some effort, but is certainly worth it when you're talking about that much cash.
As far as Teslas go, I was checking the used market a few months ago and there wasn't a single model 3 (with a clean title) available for under 30k. In fact, there really weren't any for under 34k. They seem to hold their value extremely well. I'd recommend putting it on Facebook marketplace, Craigslist, and posting it here in the marketplace classifieds.