Quoted from Chicoman:Gene Simmons is probably paid a flat fee to appear for two hours or however long. That $120 is what the convention people are charging for his autograph to make up the ca$h for having to pay him. He's probably charging between $5-10k which is an average cost for any celebrity to make an appearance at one of these shows. They all charge this amount.
Or, they pay him nothing and he keeps the cash to sign. Many celebrities are doing it that way now as they can make more money. Pay him $10k to appear or he could make $30k on his own. (I have been a guest at a number of conventions and work with the Chiller Theatre Convention in NJ)