STEPS:
1.Please first create a dummy user who will be used to do automatic approval
2.Create a approval rule using the amount for which you want to auto approve
3.Login as workflow administrator (generally it is SYSADMIN user) and go into Administration - Vacation rule
4.In the user lov, select the dummy user you defined earlier. and click on Create rule
5.In the item type - select AMS Marketing approval (note that this LOV is based on lookup - WF_RR_ITEM_TYPES meaning- WF: Routing Rule Item Types lookup type and the WF: Vacation Rules – Allow All profile option.)By default this will only have ALL or only those item type for which this user has already received notification.
6.Then Hit in Next button, and in the next screen select the notification - for budget approval
7.hit next button and in next screen, use the respond radio button and select action as Approve.and then click on apply. this is all setup you need.