This is the hardest part for an artist who is just starting to sell their work. There is some truth to the notion of "perceived value". Prices that are too low are sometimes just as bad as too high because the customer might think that you used sub-standard materials, are an amateur or that you do not perceive yourself as a good artist. If you do not believe in yourself, then how can you expect your customers to?
What are other similar artworks selling for locally? You should do some research to find that out. Visit other art shows where the artists are selling their own work and look at their prices. Ask them if the pricing is working for them then compare apples to apples.
A guideline I have seen on the Internet is $1.00 sq/ft. for an original painting. Another is number of hours at a reasonable price per hour plus materials. I applied the second guideline to a group of my paintings I thought represented my normal work, then converted to an average price per square inch that I now apply to all of my paintings. I take into consideration things like difficulty and finished quality and adjust the prices of individual pieces accordingly. If my pieces are selling too fast, I raise the prices until they stop selling and vice versa. Try adjusting your prices and see if it helps.
Next: If You Are A Painter, Do You Sell Prints Of Your Work?