Cheapest priced copy (Battlebond): $0.35 at Card Kingdom, near mint, their price list as of .
Thunder Strike 
Instant · Common · Magic 2011 · #157
Target creature gets +2/+0 and gains first strike until end of turn. (It deals combat damage before creatures without first strike.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Battlebond | 185 | Common | $0.35 | $0.49 |
| Magic 2011 | 157 | Common | $0.35 | $0.49 |
| Magic 2014 | 159 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 15 August 2010If a creature doesn’t have first strike, granting it first strike after combat damage has been dealt in the first-strike combat damage step won’t prevent it from dealing combat damage. It will still assign and deal its combat damage in the second combat damage step.
- 15 August 2010Thunder Strike can target any creature, even one that already has first strike or double strike. (If it affects such a creature, it will, in effect, just give it +2/+0.)