Treasure: I don't believe anyone has mentioned Jamesbuc's Itch.io Gems #2.
$2 minimum
Games:
-Sage Fusion 2
-Advance
-SturmFront - The Mutant War
-Alchemist Penguin
-Chucky Mendoza and the curse of the Pharaoh
-Pollen
-Gnop Gnop
-Orphan Sound of Silence

You'll probably now wonder where's the 1st Sage Fusion, since this one's the 2nd. The 1st is also available on itch.io for free here and the 2nd is the direct sequel to that one (the 1st ends on a cliffhanger), so you're advised to play the 1st one first. Due to some kind of weird coincidence I spotted the 1st one on itch a few days ago, and just finished it an hour or so ago. The 1st is an interesting combination of point-n-click (no right click actions here though) and action (battles and stuff). The world building is pretty good and one sympathizes with the characters. The 1st one also took 3-4 hours to complete (maybe even more, but no more than 6), if I'm not mistaken. So since the 2nd seems to be more of the same (and I liked the1st a lot, in case it wasn't evident), I'm personally planning to get the bundle just for that one (the game is sold by itself on itch for $2.99 so getting it on the bundle is still cheaper).

Grargar: Arcen Games weekly sale on Humble Store. Aside AI War, Bionic Dues and The Last Federation which are already here, the sale also features A Valley Without Wind 1+2, Skyward Collapse, Starward Rogue and Tidalis which aren't here yet. All the games come with both a DRM-Free build and a Steam key. In addition, A Valley Without Wind 1+2 and Tidalis come with soundtracks (both MP3 and FLAC).

Grargar: <span class="bold">The Humble Eye Candy Bundle</span>

Free
Eye Candy Flavor Pack

PWYW ($1 for Steam keys)
Human Resource Machine
Shantae: Risky's Revenge - Director's Cut (Steam/Windows-only)
A Boy and His Blob (Steam-only)
Coupon for 10% off one month of Humble Monthly for new subscribers.

BTA
Mini Metro
Mushroom 11
Towerfall Ascension

$10
Evoland 2 (No Linux)

All games come with DRM-Free builds and Mac/Linux versions except where noted above.

Grargar: <span class="bold">The Humble Eye Candy Bundle</span>

Grargar: <span class="bold">The Humble Eye Candy Bundle</span>

Free
Eye Candy Flavor Pack

PWYW ($1 for Steam keys)
Human Resource Machine
Shantae: Risky's Revenge - Director's Cut (Steam/Windows-only)
A Boy and His Blob (Steam-only)
Coupon for 10% off one month of Humble Monthly for new subscribers.

BTA
Mini Metro
Mushroom 11
Towerfall Ascension

cecil: Are soundtracks ever included anymore?

Grargar: Sometimes.

cecil: any in this bundle?

Grargar: Doesn't seem so.

cecil: Are soundtracks ever included anymore?