On a tight budget, definitely look used wherever you can. You can get some banger deals on used computers, monitors, projectors, speakers, etc.

I would reckon either a cheap laptop, mini pc, or used workstation would work as a device to play movies. Alternatively, if you happen to have a playstation, you could also use that as a dvd player.

For speakers, the Edifier speakers are pretty good value. The 1280DB is around $100 and you can always hunt for sales. Make sure to get an active speaker so then you don’t need to get a separate amplifier. If you don’t fuss about sound quality, the teeny tiny pebble speakers are decent and can be found for very cheap too.

For display, I would go for a used projector. For projectors, depending on how big your room is, try to look for short throw projectors (basically means big screen with a small distance).

Another route would be a cheap monitor, which although smaller than what a projector can output, is still quite a bit bigger than a phone screen. It would work better than a projector if you have lots of windows and tend to watch movies when there’s a lot of sunlight (if you watch movies at night and/or you don’t have many windows, projectors work fine)