I know it's a little ghetto, but couldn't you get some red patching tape from an autoparts store to tide you over until it's fixed or replaced? You can try contacting one of the guys on these boards that work at a dealership to see if they'll give you a better price. The part number is 55077891AC from what I could find. I think Bricktop2 can help you.
the cheapest I could find on the web was $61 plus shipping.
07 - 09 Jeep Wrangler Tail Light Rear Lamp - Left (Driver) 08
'09 X Unlimited, 4WD, auto, half-doors, soft-top
RC 2.5" Series II BB, JKS Quick Discos, JKS adjustable front track bar
15x8 Unique 297 (Soft 8), Goodyear MTR/Kevlar 35x12.50R15
5.13 gears, ARB front locker, Currie front shafts
Bushwacker flat flares, Rubicon rails with steps added