The jobs module is lacking the facility to create budgets for jobs and then compare the actual cost/revenue against the budget.

I would suggest adding a table similar to planning lines but called "Budgets". Budgets would then be linked to Tasks just like planning lines.

The budget could then either be entered as a simple cost/revenue budget line or could split by different dates which would allow any level of flexibility - e.g. monthly budget or a weekly budget or even a daily budget if really required.

The Tasks screen could then have "Budgetted Costs" and "Budgetted Revenue" columns with additional columns showing the variance of actual vs budget for costs and revenue.