Found lithographs listed for sale on Amazon. No Further for $450 and Ambush for $300. The prices, though, are noted for "Edition Plus 40 Artist Proofs out of 300" Since yours are part of the original 40 run, they may be worth more. I'd say you may want to get them appraised.
https://www.amazon.com/No-Further/dp/B00XLYJQFC (Ambush is in the Similar Artworks links)