When I went, a Mother+Son seemed to have the place fenced off, and asked for $6 (200 baht) to let me in. I happily paid and had a great time walking around, taking pictures, and climbing through the airplanes. It was fun climbing up the back of a 747, going up the stairs, hanging out in the cockpits, out doors, on wings, etc.
When I was there, there were no other tourists there (as I assume is usually the case). You have to be careful, as there are scraps and sharp things everywhere (though everything small seems to have been taken). One of the airplanes seemed to have someone (homeless?) sleeping in it, so I left it alone.
On the way out, the ~6 year old boy living there with his Mom asked me for another $6 before he unlocked the gate, but I told him I already paid. I argued for maybe 30 seconds and by chance another tourist showed up and the kid opened the gate for that guy and I left. Not sure what would have happened if the kid kept asking for money.
[1] http://triphackr.com/visiting-the-airplane-graveyard-in-bang...
[2] https://www.wheresidewalksend.com/bangkok-airplane-graveyard...