The only realistic option is to pick out a cheap laptop, buy a stack of them and design a replacement PPC motherboard.
An HP 255 G3 is a good choice because it can be bought retail for £200 and comes with 4GB RAM, a 500GB hard drive and a DVDRW that can all be re-used along with the case, PSU, battery and keyboard, screen.
It would probably better to get a Acube to design something around an AMCC or possibly LSI PPC SOC. I think some mid range Radeon mobility would be a good idea since we already have the drivers and a mobility chip will have the circuitry for driving the laptop screen.
The Sam460CR 1.1Ghz with 4.1FE is listed at £436.59 (£523.91 with 20% VAT) So I think Acube could do a replacement laptop board with OS4 for under £800 retail So a l think under £1100 for a complete ready to run system is a realistic possibility.