This is an AWS Lambda function that gets the various AWS costs for the previous month and publishes the result to a SNS topic. It is meant to be triggered on a monthly schedule by a CloudWatch event rule.

GetMonthlyAWSCost.js

const AWS = require('aws-sdk');

const snsTopicArn = process.env.SNSTopicArn;
const idepAccountNumbers = process.env.IDEPAWSAccountNumbers.split(',').map(item => item.trim());
const ninetyninesmeAccountNumbers = process.env.Project99SMEAWSAccountNumbers.split(',').map(item => item.trim());

AWS.config.update({ region: 'us-east-1' });
const costexplorer = new AWS.CostExplorer();

const getTotal = (params) => {
    return costexplorer.getCostAndUsage(params).promise();
};

const getIDEPTotal = (params) => {
    params.Filter = {
        And: [{
            Dimensions: {
                Key: 'LINKED_ACCOUNT',
                Values: idepAccountNumbers
            }
        }, {
            Dimensions: {
                Key: 'RECORD_TYPE',
                Values: ['Usage']
            }
        }]
    };
    return costexplorer.getCostAndUsage(params).promise();
};

const get99SMETotal = (params) => {
    params.Filter = {
        And: [{
            Dimensions: {
                Key: 'LINKED_ACCOUNT',
                Values: ninetyninesmeAccountNumbers
            }
        }, {
            Dimensions: {
                Key: 'RECORD_TYPE',
                Values: ['Usage']
            }
        }]
    };
    return costexplorer.getCostAndUsage(params).promise();
};

const getMarketplaceCost = (params) => {
    params.Filter = {
        Dimensions: {
            Key: 'BILLING_ENTITY',
            Values: ['AWS Marketplace']
        }
    };
    return costexplorer.getCostAndUsage(params).promise();
};

const getServiceCost = (params) => {
    params.Filter = {
        Not: {
            Dimensions: {
                Key: 'BILLING_ENTITY',
                Values: ['AWS Marketplace']
            }
        }
    };
    return costexplorer.getCostAndUsage(params).promise();
};

const getRefund = (params) => {
    params.Filter = {
        Dimensions: {
            Key: 'RECORD_TYPE',
            Values: ['Refund']
        }
    };
    return costexplorer.getCostAndUsage(params).promise();
};

const getSupportCost = (refund) => {
    refund.amount = -1 * refund.amount;
    return refund;
};

const parseResponse = (data) => {
    console.log(JSON.stringify(data));
    let amount = parseFloat(data["ResultsByTime"][0]["Total"]["UnblendedCost"]["Amount"]);
    let unit = data["ResultsByTime"][0]["Total"]["UnblendedCost"]["Unit"];
    let estimated = data["ResultsByTime"][0]["Estimated"];
    return { 
        unit: unit,
        amount: amount.toFixed(2),
        estimated: estimated
    };
};

const formatItemCost = (label, cost) => {
    return label + ': ' + cost.unit + ' ' + cost.amount + (cost.estimated ? '*' : '') + '\n';
};

exports.handler = (event, context, callback) => {
    const now = new Date();
    let startDate = new Date(now.getFullYear(), now.getMonth() - 1, 1);
    let endDate = new Date(now.getFullYear(), now.getMonth(), 1);
    
    let start = startDate.toISOString().slice(0, 10);
    let end = endDate.toISOString().slice(0, 10);
    
    var params = {
        Granularity: "MONTHLY",
        Metrics: ["UnblendedCost"],
        TimePeriod: {
            Start: start,
            End: end
        }
    };
    
    let getMarketplaceCostPromise = getMarketplaceCost(params);
    let getServiceCostPromise = getServiceCost(params);
    let getRefundPromise = getRefund(params);
    let getIDEPTotalPromise = getIDEPTotal(params);
    let get99SMETotalPromise = get99SMETotal(params);

    let eventText = 'Month of ' + startDate.toLocaleString('en-us', {month: "long"}) + '\n';
    
    Promise.all([getMarketplaceCostPromise, getServiceCostPromise, getRefundPromise, getIDEPTotalPromise, get99SMETotalPromise])
    .then(function (data) {
        let marketplaceCost = parseResponse(data[0]);
        let serviceCost = parseResponse(data[1]);
        let refund = parseResponse(data[2]);
        let idepCost = parseResponse(data[3]);
        let proj99smeCost = parseResponse(data[4]);

        eventText += formatItemCost('AWS Marketplace', marketplaceCost);
        eventText += formatItemCost('AWS Services', serviceCost);
        eventText += formatItemCost('AWS Support (derived from refunds)', getSupportCost(refund));
        eventText += formatItemCost('IDEP Sub-total', idepCost);
        eventText += formatItemCost('99%SME Sub-total', proj99smeCost);
        if (marketplaceCost.estimated || serviceCost.estimated || refund.estimated || idepCost.estimated || proj99smeCost.estimated) { 
            eventText += '*Values are estimated.'; 
        }
        console.log(eventText);

        AWS.config.update({ region: 'ap-southeast-1' });
        var snsParams = {
            Message: eventText, 
            Subject: "Monthly AWS Costs",
            TopicArn: snsTopicArn
        };
        var publishPromise = new AWS.SNS().publish(snsParams).promise();
        publishPromise.then(
            function(snsResponse) {
                console.log(`Message sent to topic ${snsParams.TopicArn}`);
                console.log("MessageID is " + snsResponse.MessageId);
            }).catch(
            function(err) {
                console.error(err, err.stack);
            }
        );

        callback(null, data);
    });
};