Alternately, you could go with an older, slower, possibly cheaper PCI video card as well. You could use a PCI video in combination with the AGP card. Not sure if the AGP card is missing, if you can run with a PCI video only.
ATI made a couple of PCI Radeon cards for Mac, 7000 and 9200, I think, with VGA & DVI outputs. Might be hard to find these days.