At the beginning of each upkeep, count the number of permanents. If the number is odd, until end of turn, red creatures get +1/+1 and whenever a player taps a Mountain for mana, that player adds an additional {R}. If the number is even, until end of turn, red creatures get -1/-1 and if a player taps a Mountain for mana, that Mountain produces colorless mana instead of any other type.
NM-Mint - $1.00
Lightly Played - $0.90
Moderately Played - $0.80
Heavily Played - $0.70
Damaged - $0.50
NM-Mint Non English - $1.00
Lightly Played Non English - $0.90
Moderately Played Non English - $0.80
Heavily Played Non English - $0.70
Damaged Non English - $0.50