I doubt they'll save anything. The adapter card for instance for WiFi for those Macs without WiFi, but with PCI costs $90 over what the WiFi card does and it has a PCMCIA slot inside the PCI card. And then you need to cover the cost of the specialized drivers that may or may not work with the said card. The drivers for your PCMCIA card are likely to only work in a genuine PCMCIA slot, and not one that has been adapted to. The PCI slot inside your Mac is likely slower than the PCI slot in your desktop Mac.
Without knowing if the appropriate drivers exist, you'd be playing Russian Roulette in your attempt to save money.
http://www.xlr8yourmac.com/ is a good place to lookup upgrade cards and their availability for your Mac.