[1.7.10]Multiplier for balance should be a double not int

[tytannial]

modifier = Math.max(modifier + Config.modifier, 0);
multiplier = Math.max(multiplier + Config.multiplier, 0);

cost = (base + modifier) * multiplier;
Negative multiplier is bug in those code.
Min cost should be 1 not 0, there need a check for it.
Integer multiplier seems useless in reducing materials by percentage.