How to Reduce AWS S3 Egress Costs for My Web App?

I'm developing a web application tailored for a specific scientific computing sector. Users will need to upload their data, process it, and then download it afterward. Recently, I realized that the egress costs on AWS S3 could become quite significant, especially since I've focused more on optimizing the processing rather than the potential expenses linked to data transfers.

I'm looking for methods to lower these egress fees. One idea I had was to utilize a different provider, like B2 Blaze, to serve as a caching layer. I could sync data from S3 to B2 Blaze incrementally and have B2 handle user exports. This way, S3 would stay as the main production environment for processing, while B2 would handle the egress, potentially increasing fixed costs but decreasing operational expenses.

I'm not entirely sure what other strategies might be available. Given that user workspaces could easily surpass 100GB and some datasets could even be in the terabyte range, I need to consider how data habits affect users. If clients frequently need to download projects for updates, restricting their access could deter them from using the service. Any advice on sustainable solutions for this issue would be greatly appreciated, especially options that would remain viable regardless of the user base size.