Of all the jets the Powerjet tends to command the lowest price. I guess they are not very desirable. If you want one then it would be much better to sell one of your Penguins and buy one. You'll have plenty of change for more toys.
Yes I have noticed that, I actually missed one down here a few months ago a I was still toying with the whole idea, it was as new and only $2000.00 AUD, which is really cheap for a pro line gretsch here, it only lasted a day and a half before it sold.
I think I can understand this, even though I love my Powerjet. My first two Gretsch guitars were Electromatics which I was very impressed by, so I eventually thought it was time to get a Proline. When I went to the store there were two Proline Jets in stock: a G6228FM (with modern Player's Edition features) and a G6128T-59VS (with vintage select floating bridge, elevated fingerboard extension and tone switch). I played them both and came home with the 6228. My thinking at the time was I wanted a tone control (every guitar I had has one and I use them a lot; I didn't have a G6120 yet) and I didn't really want to mess around with a floating bridge; a fixed type bridge seemed more stable.
Later on, I was able to find a G6128T-1962 which has all the vintage select features that the 59VS had which I had previously passed on. I soon found that it is a wonderful instrument. The Powerjet has several vintage select features (tone switch, elevated fingerboard, wood bridge base) which might put some people off as being archaic on a "solid" body guitar but which I now find add to its' charm. I also love the sound that comes out of the TV Jones Power'Tron pickups but maybe some Gretsch aficionados might find them less Gretsch-y than they might want.
I'm a bit disappointed to see that the Powerjet is no longer in current production but I already have mine. I guess that the G5220 now fills this sonic niche to some extent with its BlackTop Broad'Tron pickups. --- but if I see another Powerjet on the market, I'll most likely buy it.