Yeah, Either for 100 US is a good deal. Anything over 150 you must really want it. If you wait one will show up. There is always two or three PN-2's on Ebay.
As far as the PN-2 goes, Is it really any good? A lot of people say the TR-2 sounds better. Also that the range is not that good on the PN-2. That the main thing it has going for it is the panning. I like the idea of a blinking tempo light myself.
Boss should update a tremolo with some tap tempo, panning, type stuff.
I never tried the TR-2, but the PN-2 is great for stereo setups. It has both stereo inputs and outputs. You can take the stereo output from another effect like delay or chorus and run it into the PN-2 to get some panning or tremolo. Then send the PN-2 outputs to two different amps. One of my favorite pedal combos is a DC-2 and PN-2 into two different amps.