Howling Mine is the cheapest to cast, allowing for very early card draw, but its also reciprocal, thus speeding up your opponent as well
We have tons of variants on this over the years, but check out the everyone Exploration of Rites of Flourishing or the planeswalker of Jace Beleren that no one wants to kill or Font of Mythos for two cards
Enchantments have always been a less playable card type than artifacts, making Ray of Revelation a bit less exciting than Ancient Grudge historically, but Ray of Revelation is every bit as effective when needed
Rumors of it coming up for sale do occasionally crop up, such as the fake, now taken down eBay listing for $200,000 in 2017, but nothing official has been confirmed since 2001
Which explains its position as the most valuable card overall in the MTG Marvels Spider-Man set