Foamboard functions to insulate the space only. If you have basement moisture issues, the foamboard will not fix it, so if you want to save all the money you can, then don't put it in.
But if you can afford the $1/ sq. ft. for a proper 3" of polystyrene insulation board, you will notice a nice regulation of temperature, keeping it warmer in the winter.
Also think about the fact that insulation in the basement will help your house above-ground stay warmer in the wintertime as well.
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