Murphy's price on DAGR is better than anything that's ever changed hands on Ebay (I keep track) and they look to be in better shape. There are tons and tons of power cables, antennas and mounts for them out there right now too on Ebay - especially Austin Aviation who list bucketloads weekly. PM-GPS used to go on and on about DAGR "will never be offered for sale to the public", but DIA and other alphabet agencies have stopped hassling Ebay vendors of DAGR and PLGR entirely, and now there's four-five a week on there.
As others have already mentioned, there's considerable overlap between AN/PSN-11 PLGR and AN/PSN-13 DAGR installations, as fielding was done on a priority basis, and lots of weapons platforms which used GPS were left with PLGR for ages after just about everyone else had DAGR. As someone else mentioned too, AN/PSN-10 SLGR and even civilian variants of it called the Trimpack were used, especially for Desert Storm (they also used the Magellan NAV1000M and the Trimble Scout.) There were even AN/PSN-8 and AN/PSN-9s around c.1991, but the Army never had that many of those to begin with, hence the quick purchase of all the other types for the Gulf. In my own experience, AN/PSN-8 will still get a fix; AN/PSN-10 and friends will too (but the date will be wrong thanks to Y2K) - and the NAV1000 family seems to never get a fix, probably also due to the Y2K issue (or I just have a number of bad ones.) There was also the Rockwell Trooper 1991-92, but I've yet to see any pictures of them actually in use in a military context outside of Janes.
A company called 3D Marketing also has a lockable mount for the DAGR which comes in two styles: a cylinder-lock type, and a type that uses the same standard American 5200 series padlocks used to secure SINCGARS and EPLRS and bits of FBCB2. Unfortunately they've recently doubled the price since I first saw it at Shot Show.
PLGR, SLGR and DAGR are also really fun if you have a computer, as you can hook up your laptop serial port to the military GPS, and the GPS will transmit NMEA 0183 data to the laptop, which can be utilized by Google Earth and various other mapping programs to show your location and/or map your progress as you drive. I had mine rigged up to a surplus Panasonic Toughbook and later to a touchscreen computer I made up on a HMMWV FBCB2 rack to simulate FBCB2. Looked pretty cool.