I would consider selling them a "one time print copyright for a digital file for a digital print on wood". I would not charge them as much as the original print. I would charge them half the price the price of the original or negotiate a price between 100% to 0% of the original print price of the print. Even though you may not be a professional, they thought enough of your print to buy it the first time. Now you need to determine how much it is worth for a second one. If they are friends or acquaintances, you might want to consider 50% to 0% of the price of the original print.

A friend of mine took a photo to Michael's to be framed. They also asked for a copy. She signed for the work to be done. Later she went back to Michael's and there were several prints of her photo for sale that had been digitally enhanced(photoshop). Ironically I saw that beautiful photo online and showed her, not knowing it was her photo. She told me what happened. I asked her if she sued or had recourse? She said she tried but when she signed to have Michaels do the work, the receipt said in fine print that Michaels reserves the rights to modify, alter and sell said prints. I have now seen that same photo for sale in Bed, Bath and Beyond and Walmart! She got zero money for the photo. She showed me a copy of the original on her cell phone so I could see it was legit. Sickening!!!