If you want a really tight detect-band, you might consider a cheap PLL and use its lock detect output. One for older low cell band is probably all the way price compressed. But those are needier than a simple envelope detect on a bandpass filter. And maybe -too- tight.
Looking at the old LM567 datasheet and app notes might give you ideas, despite it being Mhz rather than Ghz capable. At least it was simple enough to fit in an 8-pin DIP, and better transistors can be had. There could be a similarly-simple RF detector product, this is not really my forte either....