I've looked into the licenses required, and spending upwards of 2000.00 to get them, and then purchase just ONE suppressor is a pretty minimal estimate.
Want fully auto weapons? I can get that license here in Idaho, but again, it's about 2k, and then the weapons are 10k or more! Yep, figure 10 and UP for a fully licensed auto submachine gun with a suppressor, it goes even higher than that. (So, example of a MP5 submachine gun with a suppressor is about 25k according to the local gun shop that sells them here.) Does it cost HK that much more to make that weapon? Noway, but the market is so small, and the costs to sell them so high, that the prices are insane.
Ok, that being said, how to make a cheap'o suppressor? Easy. Duct tape and a clean empty 2 liter bottle. (This is for a .22 caliber rifle.) Just slide the bottle down over the barrel till it is snug on the snout of the bottle. (Most 1022 rifles with no front sites have bull barrels, so you just slide it down a few inches, and then wrap with a few turns of duct tape to secure the bottle firmly on the end of the barrel.)
Now chamber one round, and fire it. (The bullet makes the hole you need in the pop bottle. ) Notice the very loud sounding clack-clack from the slide, and the sound of small brass hitting the ground. You might even hear the hammer fall, but I really never noticed personally.
How long does it last? Never wore out. The bottle did become very full of gray smoke, and the duct tape was a PITA to clean off my barrel later, but sound wise, the bullet sonic boom was louder than the sound of the powder burning by quite a bit. Oh, I did bump the bottle a few times, so in the end, there were more than a few holes in the bottle, but who cares? It was going into the trash anyway! And with a 30 round clip in, you adjust your aim by watching where they hit, v/s trying to aim over the bottle bulge.. LOL
What would be cool is to make one that has a large expansion chamber that hangs down under the barrel so my scope would work fine. Will have to try that someday, but have fun with trash and duct tape.
Be aware that any suppressor without the correct paperwork, fees and licenses are illegal, and it can get you fined, jailed and your weapons confiscated.. (Pretty much they can have the used duct tape and used up pop bottle... don't think the cops would see the humor in that statement however...)