Cheapest priced copy (Mirrodin Besieged): $0.35 at Card Kingdom, near mint, their price list as of .
Rally the Forces 
Instant · Common · Mirrodin Besieged · #73
Attacking creatures get +1/+0 and gain first strike until end of turn.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirrodin Besieged | 73 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 1 June 2011If Rally the Forces is cast before attackers are declared or after combat ends, it won’t do anything.
- 1 June 2011Even though Rally the Forces affects only attacking creatures, the bonus will remain for the rest of the turn.