This is a bit of a sore spot for me, so please understand that I don't want to offend anyone. This is entirely my opinion, and you can take it or leave it as you wish. Just a warning; I tend to be fairly brutal when it comes to electric shock collars.
To be perfectly frank, I think they ought to be illegal. And I'll be thrilled to tell you why.
First, I will NOT use anything on a dog that I haven't used on myself first. That includes electric shock, citronella (a smelly spray from a collar that's supposed to train dogs not to bark), choke chains, and spike collars. (Believe me, I got some odd looks walking around with a choke chain bruise on my neck. And that was just with a normal strength "correction" that most trainers consider to be perfectly acceptable.) If you've never experienced electric shock--such as that given by an e-collar--I highly recommend it. Once you've tried it, you'll never put it on your dog. It's not exactly pain that you feel, but a distinctly unpleasant sensation that you'd be willing to do pretty much anything to avoid in the future. This is, of course, why electric shock is used in aversion training, which is what an e-collar is for, and I think it's inhumane, cruel, and unnecessary.
So the collars work just like they're supposed to. You can shock your dog all day long. The problem with training in this manner is that it has behavioral "side effects". Here's an example: your dog's digging a hole in your garden. You give him a quick zot with the e-collar, and he stops digging. "Ha!" you say, "I have succeeded!" (Something less nerdy works, too.) And off you go about your business. But step into your dog's paws for a moment. Sure, he probably won't dig there anymore. But what the heck just happened to him?! He was merrily digging away, satisfying a base instinct that most dogs possess, and BAM! He's suddenly in horrifying discomfort. He knows the hold didn't do it; he's been digging there all week, and this never happened before. He knows you didn't do it; you're standing in the kitchen. He's hurt and scared and doesn't understand what's just occured. Yes, your garden is safe. But was it worth planting the seeds of what could become emotional disorders in your dog's mind?
Another example: The mailman comes every day about the same time. Every day, your dog barks at him, and lo and behold, the mailman leaves! His barking has succeeded! He's saved his pack from the evil mailman! Seriously, barking at the mailman tends to be a result of boredom, but that's another rant for another day. So you put your trusty e-collar on the dog. Next time the mailman comes, Rover takes a shock as soon as he starts barking. He may, and probably will, stop barking at the mailman. What he has learned is that the appearance of the mailman causes him pain. Barking, which in dog-speak is a very polite and hard to ignore warning, is obviously an unacceptable behavior. He is not permitted to warn the mailman away from his home. I pity that mailman the next time he has to drop a package at the door. The dog, having been taught not to warn the mailman, may just go to the next step: biting. Or he may become withdrawn from strangers, because they may cause him pain. Either way, your relationship will be damaged because you have made it clear to your dog that his communications are not acceptable.
Here's my rule of thumb for dog training: Don't do anything to your dog that you wouldn't do to your child. Even if you don't have children, you get the idea. Don't give in to "quick fixes" like e-collars, because they only cause more problems in the end. And certainly don't give those scheisters $180 to abuse your dog.
Why don't you let me try to help with your pooch? Tell me what the problem is, and I'll do everything I can think of to help. If I can't do it, then you can buy an e-collar. Just put it off for a few weeks, for your dog's sake. I'm all ears!!