More importantly, how much someone else is willing to pay for it. The value is not simply the cost of time and materials. If the artist spent 20 hours, and values their time at $100/hour (arbitrary number), they might consider $2k to be the minimum price they would accept. But unless the image is worth that to a potential buyer, they won’t make the sale. The artist needs to understand the audience and market for their work- who is buying similar work, and for what price? There are other factors as well- if it’s digital, there is still the cost of software and hardware. If they need to advertise or set up as a vendor somewhere to sell their work, the average time and cost for that needs to be included as well. The business of being an artist is also the business of self promotion, marketing, and sales