Money can be an uncomfortable topic. I would be willing to pay 60 bucks a year for SeaMonkey port.
Is that too little? Maybe I would pay $60 to get it back and $60 to keep it active. Not every release but some reasonable frequency.
I'm willing to pay $A 100 (~$US 77) to get it back and again for ongoing annual support.
However, given the responses so far, the outcome is not looking rosy.
As for why I value SeaMonkey - it is sane (to me) in the way it operates and what it does. As for the specific features that I've always valued:
* the ability to email pages or just links (File > Send page or File > Send link) from within the browser
* the extensive cookie manager
* the extensive image manager
* the extensive popup manager
* the password manager
* the email facility - Message > Edit message as new; Folder properties (eg retention settings are especially handy for mailing lists, cronjob emails etc); Message > Create filter from message; Tools > Message Filters; the fact that my current mail spool goes back to 1996 when I first started using Netscape Communicator on Windows before migrating to FreeBSD (my first FreeBSD 2.0 installation was in April 2005 according to my recently found notebook which was after Mark Williams COHERENT UNIX died and I bid farewell to UUCP for email).
* the Newsfeed facility which I use for forums, blogs and some mailing lists.
* I've never used the HTML Composer (except by accident
nor the Calendaring.
All of this in a program which has less overhead than Firefox and a more intuitive user interface.
As I also have access to macOS these days, courtesy of my stable of Mac minis the majority of which run FreeBSD, it may be that I fire up an official SeaMonkey there and move my mail spool over which would leave my FreeBSD systems as merely mail and web servers with some occasional Lazarus + Free Pascal programming. In some dark days past, I also experimented with loading my mail spool into Apple Mail which, much to my surprise, worked almost perfectly.
My preference is to continue using FreeBSD as my main desktop operating system which is why I'm prepared to stump up money for SeaMonkey after having used it daily for almost 25 years.