Wow. Thanks everyone for the great advice.
I had been warned about the heat of the Sacramento area, but i’d also been told, as one of my California-native professors says, that “It’s a dry heat.” 
You know, it never even occurred to me to check for a Youth Hostel, even though that would have been my first option ten years ago. Maybe my age is catching up with me.
Thankyou very much for this great suggestion. I’ll go off to their website now and see what i can find out. It’s certainly handy that it’s so close to the State Archives.
The only other thing i have been able to find so far is an extended stay place called Homestead Sacramento, which is at 2810 Gateway Oaks Drive, and costs about $48 a night. From what i can gather, this is a few miles north of downtown, and would probably require a bus ride to get to the archives. If anyone knows anything about this place, or about this part of town, i’d be happy to hear it.
Thanks, Antonius, for the other suggestions as well. The Yolobus sounds excellent, and you can be sure that i’ll check out the Fox and Goose. I’m not sure that i’ll have the time or the money for the side-trip to the Sierras on this trip. I may well get to spend a few days in San Francisco, however, because my girlfriend is from there and i might drop in and stay a few days with her mother (my girlfriend has to stay in Baltimore to work). I need no encouragement to spend money in SF–it’s one of my favourite cities in the world, alongside Vancouver and my home town of Sydney. The fact that i’m likely to get back to the Bay area quite frequently over the years means that the Sierras can probably wait for a later trip, when i have some cash.
Monty, you’re in Davis so i’m sure you know the area much better than i do, but it seemed to me from looking at the map that it was a little too far for someone who will not have access to a car during my stay. Is it easy to get public transport between UC Davis and downtown Sacramento? I checked out CSUS, and they do have dorm rooms, but will only rent them out to pre-arranged conference groups, and to CSUS students taking summer school. Independent researchers like me are out of luck there, i’m afraid. I looked in the Bee, but couldn’t find any decent sublets.
Thanks again for all the help. I’m off to check out the hostel now, and i’ll let you know what i find out.