UPDATE 12/2017

It seems that Buckeye Broadband has changed their game - they now appear to be taking the more intrusive approach of intercepting requests for plain HTTP URLs on first load and serving up a data usage warning in place of the original page content. If you trigger a refresh, the warning page goes away.
For the technically minded, Buckeye is intercepting the HTTP request and returning their own page with an HTTP 200 OK status code - there is no 302 redirect involved like before. Needless to say, this is even more obnoxious, and because I absolutely refuse to put up with this sort of interference with my online activities I have taken the step of routing all my traffic through an OpenVPN instance whenever possible. Try intercepting that, you anti-net-neutrality assholes.

If you're one of the unfortunate souls who has no other choice for fast internet besides Buckeye Broadband in northwest Ohio/southeast Michigan, you're probably aware of the data caps on all of their Internet plans, which are quite low compared to national providers like Comcast and AT&T (10GB of data a month for the 10Mbps plan? Are you fucking serious?) Hell, the several times I've used Comcast when I lived elsewhere were downright pleasurable compared to my current experiences with Buckeye. But that's a story for another time. In any case, the only thing worse than Buckeye's low data caps might be the absolutely shit-tastic warning messages they inject into websites you visit once you've used up 75% or more of your data allowance for the month:

They're doing this at layer 7, i.e. directly into plain HTTP streams. HTTPS isn't affected, of course, but that doesn't make this any less obnoxious, since many websites are still HTTP-only. On mobile devices, the injected Buckeye message is so large as to make many websites unusable. And don't get me started on the privacy, security, and ethical implications of such a practice.

Thankfully, suppressing these messages once and for all is a fairly straightforward task. Buckeye attempts to inject a <script> tag pointing to some JavaScript from a specific IP address: as of this writing. Simply blocking this IP address using uBlock/Adblock, your router, or null-routing it to localhost via your hosts file is sufficient to prevent the offending JavaScript from loading. I recommend the router approach as this will effectively get rid of the message on all devices connected to your network. Of course, this won't prevent Buckeye from happily charging you overage fees, but at least you won't have to deal with their obnoxious messaging ever again.