AVS Forum has one of the more reputable 'classified' sections which has a number of projector enthusiasts. In fairness, I think eBay remains one of the better places, as is Craigslist or FB Marketplace, but you need to be really open to people coming by and checking things out in person to ensure everything is legit as expected.

A quality used single projector is more likely to sell rather than a bundle, and you have to check the prices which used gear is selling for and be realistic about what you expect to receive. Runco has been out of business for a number of years now. That impacts pricing. Sony has revamped their model lineup significantly, so the 385ES, while it was $10,000 when brand new, is now selling for $1,000. That's the price you can realistically expect for it.

Also, know the make and model of whatever Denon you are selling. AL24 is a feature, not a model number. So, make sure you fire things up, see them working, and know your pricing and model numbers. Include photos, and be realistic.

The Sony: $1,000
The Christie: $150
Runco: ??? Not much since they are out of business, but maybe.
Denon AV Receiver: ??? Maybe a few hundred dollars.

At $8,000, unless you have some nice B&W speakers in the bundle, you are severely outside current market pricing.