Question about sets that involve the dollar symbol ‘$’

Hi all,

I would like to define a set of valid CAPEX units.  To this end, I wrote:

Set SI_Valid_CAPEX_Cost_Units {

    Definition: {

        data{$/kW,$/MJ}


    }

}

However, I obtain the compilation error “The symbol “$” is not expected.”  The error points to the line data{$/kW,$/MJ}. 

I can’t figure out why, since I defined another set this way:

Set PossibleUnits {

    Definition: data { g, kg, oz, j, kj, kcal };

}