It's funny you mention the prices, as the other day when I was buying fish the price differences amazed. Granted it has been decades since I started, I am still amazed at how much even "cheap" fish are these days.
Our power here goes out a lot...I swear if a butterfly lands on the line, we lose power. Just kidding, but we do really lose power quite often. I don't have fish specific generator, but we have a gas-powered portable generator. The house is wired so I can turn on certain parts and leave...
I'm not sure if it will fit for your purposes, you may have to cut the top, but I have always found Aquaclear to be the best HOB filters. They have numerous sizes to choose from as well.