How much can I realistically sell this car for? Acura CL 99?

New ANYTHING is irrelevant.

You could have a brand new engine and it wouldn't increase the value of your 21 year old car.

Kelly Blue Book shows a trade in value almost as much as you would get for scrap metal.

$500 no doubt. 

Don't try to add up all the repairs that you did, to determine a value. That was for keeping it running when you were driving it. It was part of the 300,000 miles worth of operation.  The engine runs great at 300,000 but what about next week?

Now you have a 3000 pound blob that you're trying to sell "as-is". 

I bought a 1969 Chevrolet Chevelle SS-396 in mid 1972.  It had 19,000 miles on it.  It cost $3500.  The seller asked for $1100.  That's what I paid.  That's what cars sold for back then.  A 3 year old car got 1/3 of its cost. 

Cars nowadays last much longer with much less engine problems.  People expect to get 1/3 the cost for a 10 year old car, with 150,000 miles!!  Times have changed, but a 21 year old car has a limit on its value. 

The 1999 Accura CL mildly decked out cost was $23,000.  How much value remains?

-General automotive mechanic since 1972

It's a Scrapyard Deluxe model.  Very rare....to find someone who'll pay much more than scrap value. Kelley Blue Book shows private party value about $500 but that's in the lowest condition grade they go of Fair.  I would call yours poor.

A running, dependable car is worth $1000 any day of the week.  Ask $1200 and see what happens.    

Retail value of a nice one would be around $4,000. Low retail would be around $2,000. With all that is wrong with the car and the high mileage I would think that $1,000 would be a fair price. 

300k with a bad AC?  $500.  Sell it to the first person who makes an offer.

You may ask $1,000 but be prepared to take $800 or a little less than that.