I have a version of that military flatbed for a utility trailer... these trailers typically run a hydraulic surge break setup on the pintle with manual parking breaks. It's a solid starting platform but heavy and big. You'll find that a lot of people will pull the break setup, swap the axle and wheels, and build up a top box or cover. You could always get buy using as is and build it up as you go. Find a spare tire (they use a common bolt pattern) and run with the pintle for a while. I would expect to spend an additional $1,000+ turning it into an ExPo type trailer (and easily more depending on what you want to do).
On a side note I would keep an eye on craigslist to get a feel for how much a given trailer "should" be selling for locally. Out here in Colorado a 2005 or so aluminum Silver Eagle Mgf trailer will sit at about $1,400 to $2,000 depending on condition and included accessories. The flatbeds are more rare and usually older but typically sell for around $1,000. Another option worth mentioning is to bid on a surplus auction and then title it yourself.
I'm on trailer #5 or so now (yes, I have an addiction lol), and while it's been a fun ride if I did it all over again I would have saved my pennies and jumped into a mid-level off road trailer like the Ruger or Outlander Sherpa (no longer made). I would have had it built with a removable tub so I could still use it as a utility flatbed if needed. That would have allowed for less of my time off working on trailer projects and more time enjoying the outdoors... in theory at least.
