Another workaround (that I’m looking at) is just to hire a Microsoft Azure VM, install WordPress and attach downloads to a password protected blog. You’d need to maintain the blog (update it regularly), find a plugin that secures the download and make the download directory not browsable (and hidden from search engines).
This solution will cost about $200-$300 instead of $75 from Dropbox, but it will allow you to share links with users that can be larger. Another advantage of this is that it has the power of a blog and will save you money if you have a larger Dropbox user base.