Mostly it depends on what you get the cam for off of ebay. Every camera I have built cost under $200 bucks in parts. That is after the sunk costs of the soldering iron, drill press, glue.
Boards are 40-60 bucks, cases are 20-27, glass, pipe, servo wiring, couple dollars here and there. You can get a kit not including a camera for 115 bucks, pre drilled case, python lock everything, you just put it all together.
I buy sony cams p32 p41 s40 or s600s, spent anywhere from 25-65 bucks on them. Maybe I did get one for 85 dollars once.

whitetailsupply.com is where I buy most stuff. But I also like yeti boards and snapshotsniper boards.

Here is what it looks like, generally, I change things too, for example I added external power to this cam for more pics between checks and covered this one with real douglas fir bark for concealment. You can buy camo cases too.