But there are hotels quite near the airport in PEK. They are overpriced, but where I stayed (Sino Swiss Airport Hotel, about $120/night) the service was quite good, the room was clean, and they cheerfully pick you up and drop you off at the airport, no charge.

I had a similar problem - hard to get flights from somewhere else in China to PEK in time for UA's flights. But since the within-china flights were on a completely different PNR, I wanted a long layover in PEK just in case anything went wrong. So, leaving my origin in the evening and arriving in PEK around midnight was perfect. After a nice overnight at the hotel, it was easy to roll into the airport (which is beautiful, BTW) at around 9:00 or 9:30 for the SFO flight. A totally problem-free experience.