For context on how steep the drop-off is: the base (foil-slot) versions of these same cards sit under $10 Belle & Beast [Foil] #132 is around $9 and Lilo & Stitch [Foil] #31 around $8.50
The cost-reduction ability of Sentry Bot doesn't change its mana cost or mana value, only the total cost you pay
Targeting Ramirez DePietro, Pillager makes it refund the card and the mana
Red offers Galvanic Blast, which deals double damage if Metalcraft is online, as well as Orcish Vandal, which can sacrifice artifacts to deal 2 damage to its targets
While both are readily available in many green Commander decks, if a board wipe comes down or you havent established a board position yet, you arent going to feel good about seeing it on the battlefield
Once an action card has been used, it goes into the players discard pile face-up