You've got a good, low-budget horror with some interesting twists and I think it would be pretty easy to shoot. Your first 4 pages sail by and grab interest and we immediately see our protagonist is not going to be a victim. There are some pretty awesome deaths and wounds and a couple of unexpected twists. The tension rises well into the climax. It's well written, very few typos. I'm glad to see a unique protagonist.
There are some things I would work on strengthening. There are very few moments where you let your dialogue roll. The vast majority of dialogue is broken up by action lines and descriptions. This jumped out at me right away, pages 2-3. I don't think there was an exchange in the whole screenplay that lasted more than 3 lines before you inserted an action line again. Trust your characters to breathe and trust your actors that they will pick up on the subtleties that you're writing out in the middle of their conversations. On the topic of dialogue, Stella doesn't have much. We feel for her because we see her get mistreated but she doesn't reveal much about herself which can make it harder to relate to her other than through consequence of others' actions on her.
The tone felt a little uneven to me at times, particularly around pages 40-41 with the tipping gag. Up until that point I was reading it with a pretty serious tone and then that riff pulled me out a bit. I think this story could go either way, either serious slasher or horror-comedy but I would even the tone out.
Along this line, I know it's a slasher, and your kills are pretty awesome, but your characters seem really dead or wounded then aren't and keep going. Of course Oscar is the first example and I found it unbelievable. Everyone seems to get chopped, shot, stabbed and punched and then proceed as if its "just a flesh wound." I bring this up in the context of tone because if you're going the farcical route then these things will play well as part of the comedy. If you're going the serious route, then the laws of anatomy and physics will need to be applied a bit more here (and the flesh wound line removed.)
I was expecting the "honey mustard" theme to come back in some way at the end, a little more strongly than the ranch scene. I would think this theme through. Is honey mustard a metaphor for Stella's sweet yet tart personality? Then I would need to see more personality from her to really sell this, particularly more "sweetness" (her "have an amazing day" line comes across as stiff and perfunctory like she's holding onto rage rather than being sweet.)
There are some logical pieces you'll have to figure out. The captive women scene feels a lot like Don't Breathe which you reference. On page 20 you introduce us to a missing "teenage girl", on pg 34 you show us pictures of "two girls" on page 58 we meet a "captive woman" and then on pages 85-86 it feels like the captive woman is suggesting she is the missing teenage girl from page 20. I would even all this out, the implication is they are all the same girl so I would make her age consistent. Unless you're implying she was kidnapped as a teen, which stretches believability since Stella was being bid on within minutes on page 67. Also, if it is the same girl then you are showing her face on page 20 so I would capitalize her character tag. You're also showing her on pg. 34, which would reveal that they are keeping girls in the basement since presumably the picture is of them bound (you establish this with Stella on pg. 61.)
On pg. 77 police are at the front door knocking and smiling, though we have blood on the front porch and bullet holes in the house (pg. 38) and a truck in the front yard all shot up.
Again, depending on the tone you're going after, would the sheriff be drinking in a bar rather than pursuing a murderer on the loose? Would he be able to drive if he can barely "sit up straight?" (pg. 66) Hayden sounds cheery (pg 62) but there was just a mass murder in his small town and his co-worker and boss' daughter are dead. Same with Roy on pg 63 awfully relaxed considering the urgency of the day.
Pg. 7 I would find a synonym for "mocha" since you used it in her character description. Pg. 24 a "billfold" is usually considered to be a wallet. I got a little lost on 76-77 what she was doing with the chains. I would seriously consider cutting the scene on pg. 85 after "that was for my friend" as the rest of the dialogue diffuses the power of the scene.
Pg. 30 I like the way you slow-reveal relationships. Pg. 32 love that it was a girl. Pg. 42 nice twist with Newton, adds to the tension. Pg. 45 awesome image of Stella in the window. Pg. 49 nice use of sound. Pg. 65 love the kiss. Pg. 74 nice tension!
