Rock memorabilia valuation

Hey, I’ve got two framed, signed prints by the late Storm Thorgerson (Pink Floyd artist) that I’m considering selling, as we’re tight on cash. One is “Wetback Catalogue” and the other is “Great Dance Songs”. I bought these when I met Storm around 2009. They’re very dear to me, so I’m torn.

How would I go about getting these accurately valued? Or should I hold onto these for as long as possible?