ESS Heil Air-Motion transformer model 1-D set of speakers

That is a very old loudspeaker at this point in time. I would only recommend purchasing them if you are a competent do it yourselfer with the needed skills. If you are a seller, it's really hard to say. It would depend on condition and updates. 

I am a seller with very little knowledge of these speakers.  They seem to be in excellent condition and sounded great when I last listened.

I usually check ebay before listing anything to get a low-ball price estimate. Just sell the components if shipping. Tweeters could fetch about $300 to $400 a pair, woofers $100 to $160 each depending on condition. Good luck.

@robbinsnest Used "core" value ranges greatly on the later 1D model. The prior 1C, 1B models are a little more desirable imo. Parts including Heil AMT diaphragms (brittle by now), dry crossover caps inside, stiff-cracking woofer surrounds due to age -  can be repaired and reconditioned at a cost. The value of a complete in tact set (not parted out) depends greatly on the overall cabinet wood surface condition and top grill frame condition. If you have a local audio group chapter, find them, and ask there first.   Can be fixed, re-veneered. Mint condition pair prices ranges wildly.  Restored units can take a while to sell to a fan.   

They typically sell when the right (fan) local enthusiast comes along. Damaged pairs get parted out for low prices as "core" parts. Best to sell as a complete set to a local enthusiast who knows about them, not having to ship them is key.  Be nice to local buyers and let an enthusiast take them off your hands. If you permit a few people to make offers locally, this helps to sell them faster.  A few diehards still mess with them in some areas. :) Of the remaining few, some don't mind paying a little more for extra clean units to restore. Memories.  Best of luck on the sale.