Cheapest priced copy (March of the Machine): $0.49 at Card Kingdom, near mint, their price list as of .
Baral and Kari Zev 
Legendary Creature — Human · 2/4 · Rare · March of the Machine · #302
First strike, menace
Whenever you cast your first instant or sorcery spell each turn, you may cast a spell with lesser mana value that shares a card type with it from your hand without paying its mana cost. If you don't, create First Mate Ragavan, a legendary 2/1 red Monkey Pirate creature token. It gains haste until end of turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.49 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| March of the Machine | 218 | Rare | $0.49 | $0.49 |
| March of the Machine | 302 | Rare | $0.49 | $0.49 |
| March of the Machine Promos | 218p | Rare | $0.49 | $0.79 |
| March of the Machine Promos | 218s | Rare | — | $0.59 |
| Tarkir: Dragonstorm Commander | 282 | Rare | $0.49 | — |
4 rulings from Wizards of the Coast
- 14 April 2023The spell you cast from your hand without paying its mana cost is cast during the resolution of the triggered ability. Timing restrictions of that spell based on card type are ignored. It will resolve before the spell that caused the ability to trigger.
- 14 April 2023If you cast a spell without paying its mana cost, you can’t choose to cast it for any alternative costs. You can, however, pay any additional costs. If the spell has any mandatory additional costs, you must pay those.
- 14 April 2023If the spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 14 April 2023Baral and Kari Zev will count any instant or sorcery spell you cast during a turn, even if it wasn’t on the battlefield at the time. This means if you cast an instant or sorcery spell, then Baral and Kari Zev comes under your control, its triggered ability won’t trigger that turn.