The classic yoga chair is a simple metal folding chair with the back panel knocked out, although any sturdy chair with a hard back can be used to greater or lesser effect. Shoulder Stand on the chair is a safer (for the neck) and more accessible restorative variation. You will also be able to sit with your legs through the chair and do back bends, such as Viparita Dandasana (Inverted Staff Pose).
These metal chairs can be purchased fairly cheaply. You can either knock the back panel out yourself, which will be very noisy, or you might be able to find a local hardware store that will do the work for you. Many yoga prop suppliers have pre-modified chairs available. Try Tools For Yoga or the Iyengar Yoga Institute in San Francisco.