Is there a way to install the STI rev notifier (the thing where you can set the notify RPM then it will beep) on a WRX?... Is there a kit that we can just install?... Sorry if this has been asked already.

its part of the sti gauge cluster. you would have to do a full swap, search for a forum describing how to do it

actuly you can but its not worth it. the board that the wrx uses are printed on are the same ones used in the jdm sti(pre 03). so yes if you want to put in the work to find all the right resisters that you would need, then yes it can be done. my advice is to get a jdm sti cluster for the dub-x or a usdm sti cluster. just depends on what you want it to look like after you install it.

Where can I get a usdm/jdm STI cluster (whichever is cheaper)?... how much do you think it will cost to get it installed at a shop?... and where does the STI rev beeping sound come from exactly?... Is there an embedded speaker under the gauge cluster?!....

Where can I get a usdm/jdm STI cluster (whichever is cheaper)?... how much do you think it will cost to get it installed at a shop?... and where does the STI rev beeping sound come from exactly?... Is there an embedded speaker under the gauge cluster?!....

Check out the "STI Part Out" threads. I just purchased one last week. I would just install it. It's not too difficult to do. Here's a post that will give you some idea of what's involved.

http://forums.nasioc.com/forums/showthread.php?t=1166573

Also, if you're worried about having the correct odometer reading, I would contact the guys at Tacoma Speedometer