I've been setting a budget of about $1,500 each year for the last few years since I started going way overboard for Halloween (before it was just "kinda overboard"
...) I actually do somewhat stay within that budget but only because that's a pretty huge budget and because the last 4-5 years I've been building my own decorations for a number of the big ones that I put out. There's still a lot of cost for wood, accessories, and the like but it does help somewhat. Last year was my big round of pre-made animatronics from places like Spirit Halloween and the like, so I had very little left for building my own, but it was a fantastic success nonetheless. This year I'm back to building my own again, augmenting with accessories and props, so I'm very close to budget. Next year I don't know what things are going to be like, however, as I really want to get a projector that can do the entire front of my house and use mapping software, kind of like what they do on the castle at Disney. Any projector of that capability would need to be 10-12,000 real lumens, not the made up numbers that so many companies throw around, and that's BIG money. Might have to take my kid out of college to pay for it.
Either that or I've been considering how feasible it would be to use 2 or 3 projectors spread out so they each covered part of the front, and using a laptop or something else to project 1/2 or 1/3 of the full image through each projector. That would require maybe 7-8,000 lumens per, which would drop the cost significantly. Anyone have thoughts on this?
I started attempting whole-house projection shows in 2013 so I've learned along the way. Not sure how large your house & yard are or what competing light sources you have, but you might not need that expensive. We have a new LED streetlight RIGHT over the driveway (argh!), and even then we are able to do a good moody show with 2 BenQ 1085ST projectors, one inside the garage rear projecting on a custom screen in the garage door opening, and the other under the wishing well under the front tree. We can't get the entire house since the front yard is too shallow so we have to shoot at an angle to get the most coverage, which requires pre-keystoning by angling the footage during editing. Of course you can't see much until dusk, but even Disney doesn't do their projection shows in daylight.
Halloween 2016 - Waltz of the Spiders
To compare, this is only one of the same projector straight on in the same shallow front yard. Yes the moon and the ghosts are all just one projector. Several people couldn't find the projector even when they looked since they assumed there must be more than one. I was impressed we could see the moon footage when the sky was still only dusky blue not fully dark yet.
Halloween 2015 - Day of the Dead
One more example that has more happening over the full projection area was my Christmas at Castle Arendelle last year. This show is 4 projectors: window, garage door & porch greeter are rear projected, then whole-house front projection, but only the garage & front are synced, the other 2 are independent loops from local video sources. You can see how the snowfall fades about halfway across the garage, but since I faded the edge, it's not that noticeable that it's not truly covering the entire facade:
Christmas at Castle Arendelle
Those projectors still go for ~$1000-1200 new and $600 used if you watch eBay & take a gamble. The 1085 keystones both horizontal & vertical, otherwise they are identical, use the same bulb, and the remotes & power cables are interchangeable. We added a projector each year along the way as an investment expense, not all 4 in one year! Our favorite part is the black levels are nice & dark so you don't get a gray rectangle around the edges, and even when you research advertised contrast levels, you never know until you try it in position. We have 2 BenQ1080ST & 2 BenQ1085ST now, but one of the bulbs is going, and even after a bulb replacement our 2018 show was noticeably darker than the same footage from Halloween 2016. That one projector was an eBay gamble and at least it worked great for 2 Halloweens. The ones purchased new are still going on original bulbs, even the one from 2013. Moving the dim projector into the garage balanced it better for the Christmas show.
Syncing videos is a real pain, even from a single computer outputting to multiple displays. QuickTime & VLC are off by microseconds so when they loop they eventually get out of sync. I've designed buffer time in my videos to compensate, but I can tell they're off. The only way we can sync multiple videos perfectly is using Brookshire VSA which only runs on Windows.
The mapping is always trial & error for me. I haven't found any programs yet that help enough with the actual mapping since each surface is different, especially since I work on Adobe Premiere Pro on my Mac but the show usually runs on another machine that can run Brookshire VSA software to sync with animation effects. I export a clip, convert to the avi format, test on the VSA machine, watch it projected in place, take notes & make adjustments until I get it right. Then NOTHING MOVES until after the show closes.
I was at the Winchester Mystery House panel at Midsummer Scream listening to PaintScaping.com's preview how they were working on their projection mapping show on the house, and they started by making a detailed 3D CGI model of the house, then creating the CGI animation that could act on the 3D model....however that kind of program and learning curve will need to wait until I retire from my dayjob.
Hope that helps! Good luck!