Pledges Customization & Budgets

Pledging should have additional features that allow parties to bargain/customize their pledge. For example, if your party reaches x amount of seats you will commit to pass y funding. Regardless, I think there is an issue with the fact that a party can have say 22% of seats in a legislature and be held to account for a pledge they made. In what scenario would electors realistically expect a party with such a limited amount of seats to be able to pass a budget? Moreover, I think that there should be a penalty for parties that vote against a budget that meets the pledge without having put forth an alternative budget.