Voters pushing in either direction have no advantage over their opponents. Chip costs rise sharply if a rep drops her grant near zero. To zero out an agency is the budgetary complement of dumping funds on a favorite and not supporting the other public goods one uses. The cost schedule also soars as a grant nears double the neutral level. So the practical upper limit for a grant is about 2.0 times the neutral grant.
Incentive systems are only as good as the behavior they evoke.
Since that varies from one setting to another, the system must adapt. The cost schedule below meets the seven criteria. It can cover a range of incentives from mild to severe depending on how many chips the reps start with. There probably are several excellent formulas for fair-share budget setting, just as there are for proportional representation. Experience will reveal the best formulas to give reps fair shares in setting agency budgets.