I'm in the exact same position.
OEM are expensive, and I don't know if they're really comparable to a good aftermarket light like KC or Hella (if htey made a 5" light).
Also important to me is a fog beam pattern, something close up and wide that will fill the gap below my headlights when offroading or driving through a blizzard, or whatever.
I measured my valance and the opening is 5" exactly, so I'm looking for a light just under 5", or maybe exactly 5".
Here are a couple options I've found so far:
Rampage 4.75" fog light:
Amazon.com: Rampage Products Offroad Vehicle Lighting Complete Kit - Round H3 55w Clear Fog Lights, Black Polymer Housing, Glass Lens (4.75"x5"x2.5")Kit - Complete Light System: Automotive
Bosch fog light, about 4.2" round:
Amazon.com: Bosch 0305055901 Compact 100 Clear Lens Fog Light Kit: Automotive
I've also been looking at the KC 50 series. They make a $35 (per light) version that you can find in most online stores, but I need to review the overall dimensions to make sure it will fit. KC is probably the most expensive though, but also the one I'm confident would be the best light output (they are 100w too).
I'm still looking though. I wish people had some good input on how good each of these brands are in terms of light output and beam pattern, but thats hard to find