YAMU needed an office computer see as a dog at the other one (the charger at least). So, we tried a few places, looking for the cheapest deal. A new desktop (including monitor) seems to be about Rs. 38-45,000 at, say, Unity Plaza. You can, however, get one fresh off the boat from Canada for about Rs. 22,000. So that's what we bought.
AOne is a shop in Wellawatte, across from the Savoy Theatre on Galle Road. They (and a similar shop next door) import used PC from Canada and patch them up a bit and sell them here. These are office PCs from the cold north which have been upgraded en masse.
They're not new, but we got a decent spec machine for cheap. 2.0 AMD Dual Core processor and 2 GB RAM (fast enough), 80 GB hard disk (big enough) and with a 17" monitor. After getting a WiFi USB stick from Unity Plaza for Rs. 2,400 we were good to go.
The monitor connection is a bit fiddly, but besides that it's a solid desktop running Windows XP. Good enough to work on, and the dog can't eat it. If you're looking for a bare bones, affordable PC we can recommend AOne (so far)
You can get a decent used PC (with monitor) with 3 month warranty for about Rs. 22,000, or about half the price of a new one.