Unlike other political organizations of locally elected public officials, corporations, business associations, and think tanks are full voting ALEC members, referred to as the private-interest partners.
From talking to one private-interest member, the cost of joining ALEC is just over $1,000 but to vote in one of ALEC’s task forces that make policies, the cost goes above $3,000. I suspect that a higher contribution allows for greater participation: sort of a pay-to-play model. However, no fee schedule was available. I believe that a dozen corporations paid $50,000 a piece to just sponsor ALEC’s conference, and that another 42 paid at least $10,000 for that privilege (updated).