Saw it maybe 10 years ago on letmewatchthis.com, colored and I don’t think it had any well known actors in it.
A group of collage students take a trip with their professor as part of their grade but he’s secretly planning on performing a social experiment with them. They figure out what he’s planning and turn it around on him, the students going missing one by one.
I don’t remember much of the film but I remember the ending pretty vividly. It’s just him and one student left, he’s pretty sure she’s the killer which is only affirmed to him when she reaches behind her for what he believes is a weapon. He shoots her with a harpoon gun and she falls dead, her cell phone falling to the ground, before running back to town. He runs into the first building he finds, which happens to be a bed and breakfast, and rushes inside to find the rest of his students laughing and eating around one of the tables. They ask what’s wrong, where the other student is, and the screen fades.