And Intel based Gigabit adapter would be your best bet most likely. They usually run about $30 new for the PCI-e versions, but you can snag a PCI version on Ebay for around $10 usually.
Note that PCI has a maximum theoretical throughput of 1Gbit, so having any other devices on the PCI bus will cause all devices to be slower. This is not an issue for PCI-e.