I had in internship in San Francisco and had a ~$100 bike. My bike seat and post were stolen one day. I didn't know anything about the "levels" of bikes shops, so I just went to the nearest one. Turned out to be extremely high end, probably not a single bike under $5k. The guy I talked to was so helpful, rummaged around there storage room for 20 minutes, and found me a used seat & post they had down there and just charged me $10.