A lot of money?
For a professional programmer it should be less money that they make in a day for a tool they use 365 days every year.
And whether there are free editors out there doesn't mean anything as to whether it's cheap or not. Vim and Emacs and 20 other free editors already existed when ST3 (or SlickEdit, or whatever) came out.
Yes Emacs, Vim, Notepad++, etc. have been around for years but they are/were no way near as simple to get to grips with or as smooth out-of-the-box. That is where Sublime Text really nailed it. It was simple and beautiful from the moment you ran it. It didn't need a tutorial to help you figure out how to exit ;)
Now we have Atom and VSCode (to name two) that offer that excellent experience out-of-the-box along with regular updates, built in Git integration, open source, etc.
1) emacs is crazily extensible but hard to use. Uses hacks to get the performance 2) vi(m) is extensible, fast but also hard to use 3) ST is easy to use, fast but not that extensible as emacs/atom 4)atom/vscode is extensible,easy to use but slow
Because the game you'll finish in a few weeks and forget about and the meal you'll shit in the same day, whereas the editor you'll use for years on end daily.
Now, if you find another editor (free or paid) is better and gives you just as good or even a better experience, by no means, use that.
But if one feels ST3 is better, or even just a little better, then complaining about it costing 1/40th or less of a month's salary as if its any large factor doesn't make sense.
And last time I tried, working with large files was a pita on vscode.