If i read correctly, you want to turn a notebook into a mobile wireless access point, and the cheapest AP solution would be those based on the PRISM chipset, since it comes with AP support.

Centrino based laptops are tied to Intel's Pro/Wireless and thus probably wont fit. I'm not sure if there are any notebooks with integrated 'PRISM G'

if it's just a mobile AP, consider an old notebook with PCMCIA slot, find a PCMCIA card based on PRISM II (if you dont mind 11b) and play around.

if you really want PRISM G, research wireless PCI cards or wireless router.. some manufacturers based their products on PCMCIA card solution to cut cost.. rip it apart to get the card.

have fun.