Cheapest priced copy (Conspiracy: Take the Crown): $0.35 at Card Kingdom, near mint, their price list as of .
Twin Bolt 
Instant · Common · Tarkir: Dragonstorm · #128
Twin Bolt deals 2 damage divided as you choose among one or two targets.
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Conspiracy: Take the Crown | 173 | Common | $0.35 | $0.49 |
| Dragons of Tarkir | 164 | Common | $0.35 | $0.49 |
| Tarkir: Dragonstorm | 128 | Common | $0.35 | $0.49 |
4 rulings from Wizards of the Coast
- 25 February 2015You choose whether Twin Bolt has one target that will be dealt 2 damage or two targets that will each be dealt 1 damage as you cast Twin Bolt.
- 25 February 2015If you cast Twin Bolt with two targets and one of those targets becomes illegal before Twin Bolt resolves, the remaining legal target will be dealt 1 damage. You can't change the original division of damage.
- 4 April 2025If you cast Twin Bolt with two targets and one of those targets becomes illegal before Twin Bolt resolves, the remaining legal target will be dealt 1 damage. You can’t change the original division of damage.
- 4 April 2025You choose whether Twin Bolt has one target that will be dealt 2 damage or two targets that will each be dealt 1 damage as you cast Twin Bolt.