Rifts Coalition Wars and a resurrected Rifts Core Mega bundle from Bundle of Holding. There are a lot of Rifts books and the two bundles are like 1/3th or 1/4th of the books. At least the new bundle is fairly focused on a particular campaign though you'd still need the first bundle for the core rules. There's also Savage Worlds Rifts if you'd like to play with a non-class based ruleset.

In any case I'm still too biased against Palladium and I don't really have interest other than their licensed games such as Robotech and TMNT so will skip these bundles.

Rifts Core Mega Bundle ($41)

PAL-800 Rifts Ultimate Edition (2005)
PAL-801 Rifts Sourcebook One: Revised (2007)
PAL-803 Conversion Book One - Revised (2002) - converting Palladium Fantasy and Heroes Unlimited to Rifts
PAL-805 Rifts Sourcebook Two: The Mechanoids (1992)
PAL-811 Conversion Book Two: Pantheons of the Megaverse (2005)
PAL-812 Rifts Sourcebook Three: Mindwerks (1994)
PAL-823 Rifts Index and Adventures Volume One (1996)
PAL-831 Rifts Index and Adventures Volume Two (1997)
PAL-845 Rifts Game Master Guide (2001)
PAL-848 Book of Magic (2001)
PAL-849 Rifts Adventure Guide (2002)
PAL-850 Bionics Sourcebook (2002)
PAL-852 Conversion Book Three: Dark Conversions (2002)
PAL-882 Rifts Black Market (2012)
PAL-884 Rifts Vampires (2013)
PAL-896 Rifts Bestiary Volume One (2019)

Rifts Game Master Kit (2011)

Rifts Coalition Wars Bundle ($39)

PAL-813 Rifts Mercenaries (1994)
PAL-821 Rifts World Book 11: Coalition War Campaign (1996)
PAL-828 Rifts Sourcebook 4: Coalition Navy (1997)
PAL-839 Rifts Siege on Tolkeen 1: Sedition (2000)
PAL-840 Rifts Siege on Tolkeen 2: Coalition Overkill (2000)
PAL-841 Rifts Siege on Tolkeen 3: Sorcerer's Revenge (2000)
PAL-842 Rifts Siege on Tolkeen 4: Cyber-Knights (2000)
PAL-843 Rifts Siege on Tolkeen 5: Shadows of Evil (2001)
PAL-844 Rifts Siege on Tolkeen 6: Final Siege (2001)
PAL-846 Rifts Aftermath (2002)
PAL-863 MercTown (2005)
PAL-865 Merc Ops (2005)
PAL-867 Rifts Adventure Sourcebook: Mercenary Adventures (2005)
PAL-889 Secrets of the Coalition States: Heroes of Humanity (2016)
PAL-894 Rifts Coalition Manhunters (2022)