There’s a handful of minimal launchers out there that operate the same but nothing as fully featured as Niagara.
As far as costs go, I feel like $7/year for as many updates as they make and how much I use it (on multiple devices even) is one of the more fair pricing structures.
That doesn’t answer your question though. OLauncher might be your best bet and while it isn’t the same as Niagara, I could also recommend Kvaesito.
Just here to add that depending on how obscure the game is, it could be found on My Abandonware - I’m unsure of the rules here about links and such but it’s easy enough to find and I’ve never had issues with it.