"Hinge"ing on the absurd

I'm looking for a type of hinge (at least I guess it's a hinge) but I'm afraid I'm not exactly up to date on my hinge technology or terminology. I hope you lot can help.

I need something of a hinge that latches at a 90 degree (or so) position. I'm kind of thinking of something vaguely along the lines of the kind of hinges / latches that used to be (still are?) found on folding card tables, etc. You know...where there's a post that slides along a track and then pops into a detent at the end of travel. To free it you'd push down near the post. But it doesn't have to be precisely this sort of hinge. I'm open to any ideas.

I'm mounting to two flat surfaces and so far the only thing similar item to the above that I've come across is made to mount into a hollow table leg. Plus ideally this really needs to be a low-cost item (ain't it always the way?)

Any suggestions?