As with any other products, the costs will vary depending on what you want to get. The price range will be as wide as the variety of models out there. You can opt for a small one to a larger more powerful one depending on your budget. Of course, you need to keep in mind that as with anything else in life, you get what you pay for and most times if you choose a cheap model, you will not get the high quality you are expecting.
Keep in mind your protecting your life or the life of a loved one.