In addition to controlling your spend in Hotel Ads with the bidding system, you can also control your budget by setting a cap on your daily spend.
When you set a spending cap, the limit is applied to the entire account or sub account. You can set both the value and the currency of the cap with the Budgets API.
The minimum value for the daily spending cap is $100 USD. Any value between $.01 and $99.99 is interpreted as a cap of $100 USD.
For an example of setting a spending cap and max bid cap with the Budgets 2.0 API, see Budgets 2.0 API.