Can a player cast Angelic Purge targetting Demonic Pact, sacrificing the same Demonic Pact as part of the cost of casting Angelic Purge?

I assume it is similar to the ruling on Bone Splinters, but just wanting confirmation.

You could choose to target the creature you’re going to sacrifice to pay for Bone Splinters. First you choose the target (at which time it’s still on the battlefield), then you pay the costs (at which time you sacrifice it). The spell will be countered.

Yes, just as with Bone Splinters, it's legal to cast Angelic Purge targeting the artifact, creature, or enchantment that is sacrificed to pay its additional cost.

This happens because targets are chosen for a spell or ability (601.2c) before the cost of that spell or ability is paid. (601.2h) At the time you choose targets for your Purge, whatever hapless permanent you intend to sacrifice is still on the battlefield, so it's just as legal a choice as any other.