Each drawing must be discussed individually for price. For a basic idea, a Bust drawing on 8.5" x 11" is about $500. Full figures are $1000. There are many choices in between and larger sizes as well. Drawings on blank cover comics are slightly more expensive than the ones on paper due to their collectable value, and resale value.
This list is just a general idea. All prices are subject to change. All emails should be sent to firstname.lastname@example.org where Neal's son, Jason, will be happy to make arrangements for your commission with Neal. There is a wide variety of original art available on http://www.nealadamsstore.com