San Cristobal has gotten a lot pricier since 1990 or even 2000, but it's still very reasonable. We stayed at Le Gite de Sol http://www.legitedelsol.com/ which is a Posada/B&B/Hostel
Since there were 2 of us (and one was child) we stayed in the Hostel dorm rooms. I believe they keep the main location for quiet couples and you get a room with a bathroom.
At first I wasn't to impressed and it felt a bit like a jail cell, but it had really nice warm blankets, was very clean and we could use the internet. The people working there just accepted us like family and so it made all the difference. The owners are Quebecois-Mexican and speak French, English & Spanish so that is handy as my Spanish was pretty rusty. We didn't see much of the owners, but the staff in the dorm were excellent!!
The markets are fantastic in San Cristobal. This is wear to buy all those beautiful hand embroidered blouses, dresses and bags. This is the place to buy all the wonderful keepsakes and souvenirs for friends and family. That said, your pack may be a lot fuller and so you may want to make this, one your last destinations.
I budgeted a $100 Cdn for clothes and souvenirs and it went a long way. It was wonderful. Wonderful because you get such great stuff but your actually helping the people that made it. I always made a point of buying from a mother and child.
The Zocalo is a wonderful place to treat yourself to a cappochino and treat. It's great place to people watch and soak up the beautiful atmosphere just listening to the music and relaxing after a great day exploring the markets and shops.