On the AdWords API perspective, you could use the
Budget Performance Report which includes statistics aggregated by default at the budget level. However, this report type is based on your shared budget. To retrieve budgets for an account, you can use
BudgetOrderService. The
BudgetOrderService.get() method can be used to fetch the
spendingLimit of the client account. Also, please note that BudgetOrderService is available only to whitelisted AdWords manager accounts.