In the horror / thriller genre, name means nothing from what I can tell.
Just watched Maniac with Elijah Wood and can tell you his name did NOTHING for that movie. 24k at the BO for 6 million $ movie? Come on man.
Not true. Names are important in ALL genres. The first thing a buyer or a sales agent will ask is "Who's in it?" that's the bottom line, whether it's action, thriller, horror, family, drama etc. Maybe the only exception being found footage horror, since it's common to have unknowns in these kinds of movies, but in that case the buyer might ask "Who directed it?" or "Who produced it?" so they can put something like
From the producers of Paranormal Activity on the poster.
Regarding Maniac, I would say that having Elijah Wood in it played a major role in selling the movie. It's a re-make of a cult classic from the 80's, without a marketable name on the poster they would have had a hard time selling it.
Looking at the box office gross tells nothing, since it's a limited release. Maniac is the kind of a movie you sell territory by territory and it'll get released straight to DVD and VOD in most markets.
I don't agree that you attack social media before and during shooting. What, you will get maybe 500 people to follow what you do?
You can get way more followers than that if the movie is something that interests people, especially if it's a niche market, and horror definitely has it's hardcore fans.
Getting followers on social media is practically free, but it takes a lot of time.
You said that your Plan B was to self distribute, getting followers and fans online is crucial for that, how can you self distribute your finished movie is nobody knows about it?
If you get a significant amount of followers, that can also help you in selling the movie, to a point. A no name horror movie with 100k Facebook fans certainly looks a lot better to a buyer than a no name horror movie with no Facebook likes.
That way the buyer at least knows that there is an audience out there for your movie.
This is especially important if you go through an aggregator to get your movie on VOD services, since they rely on YOU to market your movie, they're just the middleman.
Having said that, having names in your movie is more important than Social Media.
If you're against getting any names in your movie, I would suggest that you lower your budget, since it will be
very hard, if not impossible, to get $150k worth of sales for a no-name horror/thriller in this day and age.
However if I were you, I would contact sales agents and pitch the movie to them, throw some names around and ask if they bring anything to the table, this way you can get a dialogue going and they might tell you what names are good for your genre and budget range, and what names are not.
Believe me, you do not want to make your movie first and then start selling it. You need to make sure that the movie you make, the package that you have, genre, script, names etc. is sellable in the marketplace.
$50k is a decent amount for name talent on a $150k budget, you should get a couple of decent names on that.
Youd be surprised to hear who you can get for $15k a week.
And yes, definitely stay away from the Eric Roberts' and the Michael Madsen's, but there are plenty of other names who are willing to work who don't leave a bad taste in buyers' mouths.