Provides that major political parties, as defined in RCW 29A.04.086, shall pay for all costs associated with partisan primaries, as described in RCW 29A.52.111. Costs shall be divided equally among the parties including a reasonable amount for administrative costs. The secretary of state shall adopt by rule the calculation for assessment of each party's ratable share of administrative costs pursuant to chapter 34.05 RCW. The county auditor shall certify the costs to the county treasurer with a copy to be delivered to the political parties. Upon receipt of such certification, each party must pay its share to the county's current expense fund or to the county election reserve fund if such a fund is established.