Bottle opener keychains are often unique and (should be) always functional. If you find yourself with one that is not functional, it is probably broken, so replace that thing!
I like a cool bottle opening keychain. Who wouldn't!
There are ways to save on bottle opening keychains, but the nice thing about this item is it starts out at a nice, low price in the first place. If price is the foremost concern for you in buying a new keychain top-popper, then you need only go here and sort the list by price. You will find something suitable there, I am certain.
Out there in the bricks-and-mortar, water-and-air world, the way to save on a keychain bottle opener is to go to a dollar store -- one of those places where everything is priced at a buck. Somewhere there, you should be able to find a cheap keychain with a bottle opener on it. Beware though, it will likely not be the coolest one you have ever seen. Sure, it will be cheep and (likely) functional, but will it be cool? Probably not.
Now, if free is the name of the game, and you have patience abounding, you can wait for a free keychain with bottle opener. Here is how: I imagine like many locales, some type of "fair" comes through your area on a seasonal basis. For me, I know I can get a neat keychain bottle opener -- likely for free -- at the brewers' festival that happens in my city every July. Additionally, state fairs are great places for companies to promote their wares. Often at state fairs, these companies are all in one place -- corralled, if you will -- in one section of the fairgrounds. I am sure you can find one or two booths at your fair where a company is happy to hand out keychain bottle openers with their logo for free. (Now, you need only worry about the price for admittance to the fair.)
Be advised, those bottle openers will not be "cool" (most likely), but they will be free, and that is usually a condition on the "cool side".