Hi Kate,
Pricing is always a tough topic. These drawings are very well done and should not be under-priced, that's for sure. But pricing has many factors: cost of time, materials, space, utilities, as well as artist demand. What I mean is that an artist who consistently sells his/her work for a certain price is more able to price their artwork at that price, as opposed to an artist who has never sold their work.
Look into this. What are comparable artists to you in that gallery or similar galleries in that area selling their work for. Look for artwork of similar quality from artists of similar name recognition/brand. That might be a good start.
all the best,
Joe