Seen as base64 won't help, and enabling compression won't help much, you could always use a content delivery network (CDN).
Chances are you can get a better deal using a CDN than your current service provider, but it really does depend on your current deal.
Personally, I use Cloudflare. Along with their protection (which I don't really need) they cache certain types of requests, such as images.
If these images are static you should increase your Expires
to years or even decades, but that will only affect returning visitors or caches. Cloudflare should take a significant load off your server. In some circumstances the load (bandwidth) on my server has been reduced by 50% - which is nice.
Cloudflare has a free tier which I think you might be interested in.
Test everything thoroughly before using any solution.