Can you give an example image? I usually use the convert tool that comes with imagemagick (on linux) and fiddle with the quality/compression %'s
Some alternatives (Free/Cheap):
https://cloudinary.com/
https://www.blitline.com/v3/home
https://libpixel.com/
https://transloadit.com/
https://www.gumlet.com/
https://imagekit.io/
You could also write a script to download the converted image from imgix and push it your cdn.