May be of interest to Mac owners. Old style bluetooth keyboard for £19 instore at Tesco - Bristol Hengrove. Had about 5 in the clearance section. Couldn't see any online so assume instore only. Seems quite solidly built.
Did manage to get it working with a dell 1525 running vista but needs to be paired again on re boot so probably not worth it for PC users. Had thought it may be an option with the recent Acer Revo offer with a usb bluetooth dongle.