Short of making something your self - I would look at the mesa 5i25. The 5i25 + 7i77 that would be $239ish for the kit.
That gives you
PCI Anything I/O – 34/ I/O bits LX9 Spartan6 FPGA
6 axis analog servo interface - 48 isolated I/O for 25 pin Anything I/O
And that is expandable.
I don't know if you can get much cheaper than that. (but may be overkill for what you are doing)
You could do a 7I43-P with a 7i33 which gives you 4 analog servo interface and some unisolated i/o for $79+$69 but that is a parallel port interface instead of pci.
Other supported hardware