Go to ebay and buy a cheap old made by ATI card for $5.
MAME doesn't need anything fancy, an old 4 or 8MB card will work fine. I have an old rage II card I got off ebay that I use in my cab with a 27" toshiba and it works great.
Not exactly true. Mame32 and all the Windows variants DO like extra hardware power if you start playing around with all the features like hardware stretch, scanlines/rgb effects and many other things that require DirectX/3d compliant video cards with tons of memory (32-64meg)
If however you use AdvanceMame out to an arcade monitor, or even Dos mame, then you don't need the extra power as they don't do all the funky stuff with the video, they output at a 1:1 ratio for the most part. I used a 4 meg old PCI card and it worked great on AdvanceMame to an arcade monitor, but wouldn't work at all with any version of Mame past about .54 in Windows.
So it all depends on:
Windows vs Dos vs Unix
PC Multi sync monitor vs Arcade Monitor
Mame version (old or new)
Video effects such as hardware stretch, blur, rgb effects, scanlines vs 1:1 output
Mame exe type (Dos Mame, Unix Mame, Mac Mame, Arcade(Advance)Mame, Mame32, Mame32Plus, etc..)
Taken together determine your graphics (and CPU) requirements.