Ammit Eternal - $3.99
So far, Ammit Eternal is the biggest test for Afflict in competitive play. I realize that the downside on Ammit Eternal is real—cards that give your opponent extra control over a combat situation tend to play out worse than we think they will—but I wouldn't be shocked if that doesn't end up mattering here. A 5/5 for three that can deal damage on a stalled battlefield? And it has a relevant creature type? Ammit Eternal has the chance to be a multi-deck staple, and that's the sort of upside I look for when I'm chasing specs in a new set. $4 for a non-mythic rare is too steep to buy in blindly, but get your set ASAP if the pros start muttering about how good this is.
Endless Sands - $1.99
Endless Sands might be my favorite card in Hour of Devastation. I'm going to try to find a slot for it in most of the Commander decks I own, and I'll be buying a bunch of foils ASAP. A gorgeous Noah Bradley card that's good in almost every slow and grindy casual deck ever made? The long-term value is going to be absurd. Get two. Get five. Get ten.
In terms of competitive play, Endless Sands is great in a slow format and almost unplayable in a fast one. If there's a pure control deck or two, this will show up as a late-game card that can sit there and grind incremental value during bad attacks, removal fights, etc. I doubt it'll be played enough to get the price above $3-$4 at the absolute max, which is why I'm focusing on foils. Best-case, Standard play drives the price of those up too. Worst-case, casual interest will still keep the value high.
Hollow One - $1.99
I don't know what Standard deck actually wants to focus on Hollow One, but any card that does this good of a Myr Enforcer impersonation is worth a second look. The dedicated cycling decks prefer to run at instant speed, though, so I'm not sure this plays well with, say, Drake Haven. Maybe it'll find a home with all those cycling Deserts?
Hollow One has some real potential in Modern, though, where it can come down incredibly early in Living End. Even if it's just a sideboard card, the current $2 price tag seems fair. If you think there's any upside in Standard at all, it's worth pre-ordering a set.
Hour of Promise - $1.99
Hour of Promise is another really safe spec thanks to how great it is in casual play. You probably aren't snagging Deserts in Commander, but a ramp spell that can get any two lands—not just basics—is going to see a ton of casual play. $2 is probably pretty close to this card's long-term floor, and it's the sort of spell that ends up at $5-$6 if it isn't reprinted on a regular basis.
In terms of competitive play, Hour of Promise is going to slot into any ramp deck that may or may not emerge in the next iteration of Standard. Could Hour of Promise into double Shrine of the Forsaken Gods into Ulamog, the Ceaseless Hunger be the new way to go over the top? I'm not totally convinced, but I'm still willing to take a gamble at Hour of Promise's current retail price.
Hour of Eternity - $1.99
Hour of Eternity is another way to get Ulamog onto the battlefield super-early, though it'll only be a 4/4 and you'll need, like, a lot of blue mana.
In all seriousness, the mana cost on Hour of Eternity is probably a bridge too far for the card's constructed aspirations. Not only do you need triple blue, but you have to double up on X. Oh—and you need to find a way to get your interesting critters into the graveyard somehow. And you have to be okay with them coming back in an underpowered form. There might be some corner-case casual interest here, but this will be a bulk rare.
Kefnet's Last Word - $1.99
You're not going to want to use Kefnet's Last Word very often—losing an untap step is very costly, even if you're getting a two-for-one out of the deal. That said, there are certainly going to be some matchups where you can either use this to steal a finisher or deal with some crucial effect that would otherwise just kill you. Kefnet's Last Word is unlikely to be a metagame-warping card, but I bet it will see enough play to stay in the $2 range.
Hazoret's Undying Fury - $1.49
Warp World is one of my favorite cards of all time, and I still don't get the love for Hazoret's Undying Fury. Not only can't you stack your library, but you can't even cast any of the cool high-CMC stuff that this effect might reveal. Oh, and then your lands are tapped next turn. I suppose there's a tiny chance that Hazoret's Undying Fury will end up as a cog in some interesting new Storm deck, but I feel like WotC worked so hard to make sure that this card can't be broken that they forgot to make sure it was still interesting and fun. Future bulk rare.
Chaos Maw - $0.99
A ramp deck might want a couple of these between the maindeck and the sideboard as a way to deal with token strategies and some aggressive decks. That shouldn't keep it from rising over a buck, though.
Imminent Doom - $0.99
All too often, you'll just play this, wait around, and die. Your doom won't be imminent, but it'll happen nonetheless. Future bulk rare.