I have the Elise Parts front splitter. Made of fiber-glass as far as I know. Comes gel coated black. We installed it with a piece of Alumalite (aka Alumacore even if they're slightly different) mounted underneath and extending a few inches out (recently cut down quite a bit) and shored up from under the car to the chassis and it's rock solid.
Out the door I think it was probably $350ish for both parts combined with some drilling and hardware from home-cheapo.
Here's a pic from before I trimmed it down a bit.
And when I trimmed it down I took off both pieces and did a better job matching colors. The above pic is straight plasti-dip on both parts, I've since painted both Satan black. Yes Satan, not satin.