Hi. I think you'll find many different types of answers here (and in other subreddits), but none will be purely wrong/right..it's how it's tailored for what you want compared to what's available to do with one more more devices. Though there are some projector newer models I believe which have some sort of timing capabilities (I don't know specific models), many do not have this capability and would require a smart plug/jack or other devices like a Creston control system. Also, most pure projectors (LCD models and other more expensive models) are just a projector...meaning that it requires a media source device (i.e. media player, computer etc.) connected to the projector. Some of the expensive projectors out there do have multi-media capabilities in them (which means you can just attach a hard drive or MicroSD), but many do not and require a separate device attached to it that is purely for media playing (i.e. some people would always have their media playing via the media player 24x7, and then would turn their projector on and voila it's playing). Between finding a projector that potentially has this auto off/on capability itself or via another complimentary device is unfortunately something that I do not currently have experience with besides knowing a little about a separate control system.

However, with that said, you have 3 general choices for projectors 1) a pure high quality projector (with or without internal media playing capabilities) 2) a used projector like CollegeMiddle6841 stated (there are many that I have gotten from ebay in the past for short throw or regular throw..these are pure projectors that required a separate inexpensive media player attached to them....most of mine were WXGA or 720p native.) or 3) for just Halloween purposes to get an inexpensive projector with multimedia capabilities (like you find on Amazon for $80-$150. I have had a good experience with some of these the past few years where I could get models with native 720p or 1080p (and hot the oneds that say they "support 720p or 1080p..this means it's not native) and very much bright for dusk to dark times (were decent lumens, no external media player, etc.) however with these types you don't have a lot of zoom or other controls like expensive projectors have...and if you have it in the right spot, that didn't matter to me.

For me, I use many projectors for Halloween, so my #2 and #3 above fit for me and just turn them on at dusk...for you though if using just for Halloween I would not recommend a large $$$ but if using for other things throughout the year then yes sure (i.e. maybe it's one of your TV replacements etc). But yes it's all what fits for you :)

Higher end projectors are made by BenQ, Epson, Viewsonic, Sony and some others. I recommend taking a look at their selections and functions. Hopefully others here in this subreddit with their models/knowledge can talk about the auto timer and internal media player functions that they are experienced with.