Well, look what I found on Steam: 8 Eyes from the NES! $7 seems like a fair price to me and I believe that you get a NES ROM included with the purchase, making it applicable to your NES / Famicom emulator of choice. I find a PC release (even if emulated instead of a native port) surprising given that 8 Eyes is Castlevania 2-like, uncommon, and quite difficult. It is just not something with a big fan following.

As it turns out, the publisher on Steam is Piko Interactive, LLC. As a matter of fact, Piko has about 50 games with them listed as publisher on Steam. Looking at the catalog, most of them could be classified as "8-bit and 16-bit games for consoles and computers from back-in-the-day without big fan followings." So while it is a bit odd to focus on publishing games that are mostly mediocre and largely forgotten, it is nice to see that these games are being made available as digital downloads for reasonable prices.