From Synapse RF Engine to PIC
Micrchip has a interactive selector guide for PICs.  You select ranges of parameters you care about, and it lists the PICs that meet the criteria sorted by price or another parameter of your choosing.  I think it's called "MAPS".  Look around on their site.  I think it will be easy to find.

If all you want to do is turn on a light based on a digital output, you don't need a microcontroller.  Some digital outputs have enough current capability to drive LEDs directly, or you can use a transistor and one or two resistors to drive a LED from any digital output.