For me personally, $150 seems obscenely high. Especially considering it would be far more economical to just buy the DVD. The cost is high enough that I would genuinely feel quite guilty for making my community pay that much. Ironically, I would feel no such guilt for torrenting the movie at that point.

I get that the infrastructure for streaming isn't cheap, and neither are the licensing fees, but this feels like price gouging. I know price gouging is a specific legal term but I'm speaking in the vernacular sense.

I understand where you're coming from.

I also understand that my library has a lot more data to make the decision than my feeling of guilt. There's no need to speculate. Email your library and ask them:

"Would you prefer I stream title X from Kanopy, or check out the DVD?"

And also ask

"Would you prefer I stream title Y from Kanopy, for which you don't carry the DVD?"

Feel free to provide the context, expressing concerns that it'll potentially cost them over $150, and you're worried that they are being abused by Kanopy.

If the library's not willing to tell me to prefer the DVD, then I'm not concerned.

$150 does seem very steep… given these numbers, I would feel a lot better simply buying films to donate to my library.

Be aware that very little you donate to the library ends up on the shelves. Most of the time they sell whatever you donate (e.g. "Friends of Library sales")