$100 is one of the manzai bgms found in Hyperdimension Neptunia Mk2. It is one of the casual manzai themes, along with Lite Light, that are used at the low-energy segments of the cutscenes. Apparently, this song was so fucking godlike that Compile Heart & friends decided to put it in like EVERY FUCKING GAME since its inception.
There is actually a reason why this song is called $100. Back during the development of Hyperdimension Neptunia, the deadline was steadily approaching, but despite being in development for 10 years, it had absolutely no music. Compile Heart had no composers who could create the ambitious 50-track OST that they had planned on including in the game. But then, one day, series artist Tsunako picked up some dude off of the streets, and brought him home to Compile Heart. That man was Kenji Kaneko, a composer; exactly who Compile Heart was searching for all those years. Upon hearing that he was a composer, CEO of Compile Heart, Moo Niitani hired him on the spot. Mr. Kaneko was tasked with composing the entire soundtrack for in a single week, and the amount of money he was offered for his services... was $100. $100 ultimately was the final sound budget for that game, and it was paid in US dollars (in cash) to Mr. Kaneko after the game was completed. This upset Mr. Kaneko greatly. Compile Heart not only barely paid him for his work, they barely gave him any time to work with, not to mention he was paid in fucking US dollars, when he's a Japanese dude who can only make use out of Japanese yen. During this one week, Mr. Kaneko worked hard with no breaks and no sleep to churn out a whopping 50 tracks for the game. While he met the deadline with all of the tracks, he didn't finish any of them, but since Compile Heart was pressed for time and money, they had to ship the game with the as of yet unfinished OST Mr. Kaneko had composed. The next day, Mr. Kaneko brought in his resignation form to his boss, Mr. Niitani. He wanted to quit because he had felt mistreated about the whle Hyperdimension Neptunia OST situation. But, Mr. Niitani was desperate to keep Mr. Kaneko around. "Nobody else will work with this company," said Mr. Niitani, "Please understand, Kaneko-san, we need you and your musical capability! You're the only one we can rely on!" And he offered Mr. Kaneko a much more proper salary: $100... per track! Mr. Kaneko still felt miffed about being paid in US dollars, but he begrudingly accepted Mr. Niitani's offer. He was homeless after all, so he couldn't really refuse an offer like that. After accepting this deal, the first thing Mr. Kaneko did was compose this song for Hyperdimension Neptunia Mk2, and he packed all of his frustration with the company into its title, saltily naming it after his salary: $100.