Is There Such A Thing As A Content Cache, Like SimpleCDN But Not So Sophisticated?

I have a site where our budget is very constrained, and we're maxing out our unmetered pipe. The majority of the bandwidth is taken up by an active forum.

I offloaded most of the static content (images, .js, .css files) to a CDN (SimpleCDN) which I've been pretty happy with, the costs are very reasonable and fit within our limited budget.

They offered a service where if the content was not found on their network, it would check on our server for the file, retrieve it, and then serve it up from then on. Which was perfect for us as it allows us to use the CDN to serve image files uploaded by users in such a way that it's transparent to the end user.

However they're discontinuing this service, and though they're offering a similar service (based on rsync), they're charging $150 setup fee! So basically I have to pay $150 to keep using the service I've been using for a while. Which I can't really do.

So I'm trying to think of alternatives. I don't think I really need a full bore CDN, while we do have users from around the world, it's not a business site so a few ms isn't going to be the end of the world.

I just need a file hosting solution that has decent performance and fairly inexpensive bandwidth.

It's only 100-200GB / month maybe. At SimpleCDN that was only costing $8 / month.

I looked at Amazon, but they charge 1 cent for 10,000 requests which for us adds up very fast.

I'd almost think of just signing up for a Dreamhost account, but I would think using them to host just our images probably goes against their ToS.