Cloudinary, Imgix, Uploadcare (which I' working for) and others save you money because you don't have to develop and maintain these moving parts. You have to constantly check what's happening with browsers, what formats/encoders are available and which are the best etc.

It's classic build vs. buy dilemma. In majority of cases it's much more cost effective to buy.

BTW, Uploadcare doesn't charge for file processing at all, only for CDN traffic. So you can create as much image variants as you need.