what is a simple inexpensive way to add a little (maybe 1/4 lb) weight to the muzzle of a rifle that is muzzle light?

Change the barrel!

Sticking something at the end of the barrel sounds awful!

Yeah, just duct tape a wheel weight to the end.
Or thread it for a muzzle brake. Even a dummy one with no ports.

Ruger provides a nice dummy Brake of same length and maybe weight as their brake for the FTW rifles. I leave the dummy mounted as 1, I don't need or like a brake but 2 I like the muzzle weight and swing of that now as mounted 26" barrel.

However, threading your barrel might not be simple or inexpensive, depending on your definition of such things. It is simple threading though.
Whatever you do, don't let any local tractor mechanic with a die thread your barrel.
I might have seen weights that are held on with set screws. Or I might have dreamed that. Or you could epoxy one on; a round one with a hole in the middle. That would be simple and cheap. I mean inexpensive.

How about adding to the front of the stock?

The bubba in me says wrap some lead wire around it coated with epoxy.

As stated above one could hollow out the forend. and bed some lead shot into the space