An example CloudFormation template for an AWS Budget with an alarm

budget.json

{
  "Description": "A Budget, with alarm, to monitor My Component",
  "Resources": {
    "EmailTopic": {
      "Type": "AWS::SNS::Topic",
      "Properties": {
        "Subscription": [
          {
            "Endpoint": "bill.bob@gmail.com",
            "Protocol": "email"
          }
        ]
      }
    },
    "EmailTopicPolicy": {
      "Type": "AWS::SNS::TopicPolicy",
      "Properties": {
        "PolicyDocument": {
          "Statement": [
            {
              "Effect": "Allow",
              "Principal": {
                "Service": "budgets.amazonaws.com"
              },
              "Action": "sns:Publish",
              "Resource": {
                "Ref": "EmailTopic"
              }
            }
          ]
        },
        "Topics": [
          {
            "Ref": "EmailTopic"
          }
        ]
      }
    },
    "Budget": {
      "Type": "AWS::Budgets::Budget",
      "Properties": {
        "NotificationsWithSubscribers": [
          {
            "Subscribers": [
              {
                "SubscriptionType": "SNS",
                "Address": {
                  "Ref": "EmailTopic"
                }
              }
            ],
            "Notification": {
              "ComparisonOperator": "GREATER_THAN",
              "NotificationType": "FORECASTED",
              "Threshold": "100",
              "ThresholdType": "PERCENTAGE"
            }
          }
        ],
        "Budget": {
          "BudgetName": "my-first-budget",
          "BudgetLimit": {
            "Amount": "100",
            "Unit": "USD"
          },
          "TimeUnit": "MONTHLY",
          "BudgetType": "COST",
          "CostFilters": {
            "TagKeyValue": [
              "user:<TAG_NAME>$<TAG_VALUE>"
            ]
          }
        }
      }
    }
  }
}