>Can anybody recommend a good, comfortable, supportive, and relatively inexpensive office chair?

My biggest problem was being hunched over a keyboard many hours a day. The root of the problem was not the chair but a lack of exercise of the other back and shoulder muscles. Appropriate exercises cleared this problem after the first week. Otherwise, go to large Office supply store. They usually have chairs out on the floor for you to try out.

Stretching exercise you can do at your desk and regular breaks usually do the trick. And they are free.