Using a serial null-modem cable linked to a PC running Multilink isn't as slow as you'd think. At least the difference in noticeable speed is negligible. For things like IRC it's perfectly fast enough, and for web browsing the speed isn't much different because you still have to wait most of the time for the images and pages to decode with the slow CPU. I use many Amigas online using various setups and I recommend you try using this method first before shelling out for a rare network card.