In UK we have some of the most restrictive firearms laws in the world which, I might add, hacks me off greatly. But, once a person gets a firearms certificate, sound moderators are no problem to acquire, if you can provide a good reason for having one. Hunting is generally a good reason.
So, I can buy a SAK brand rimfire moderator for about £36, ($50?). They are most effective on rifles, even with barrels as short as 12". I wouldn't know about pistols, as they aren't allowed at all here (with very, very, few exceptions) There are many other brands about, ranging from £25 to about £120. Few are much better than the SAK though.
Centrefire moderators are available from about £150 upwards. While they do not remove the supersonic crack, they are damned effective, or at least the good ones are. On my .223 Steyr Scout, I do not need any hearing protection when shooting. A friend at the range has a very moderately sized (smaller than mine) moderator on his Remington .308, and it would certainly be quite tolerable in the field, but it's just a little louder than mine on the ,223.
I would be interested in a summary of the situation in the US on sound moderators. Costs and designs, particularly for ,22 rimfire.