We have seen many cheap options at the store, from $5, but this really comes true, you get what you pay for. The quality of the lens is most of the time reflected on the price.
So how much to spend?
The next tear up. The Pixter. a bit pricey, cant really tell the difference of the quality of the lens, the attachment method seems a bit better if your phone is without a case and is iPhone, other work, not sure if they adjust as fast. The FishEye is not great, too much distortion . But if your are going for wide angle, just stay with the Pixter.
Yes you will spend a pretty penny for these. Really? how much are you going to inconvenience yourself to take macros and telephotos.? by the time you spend this amount and have to carry the extra case with attachments, might as well get a brand new camera. And if you are spending the money, but still want something portable, go for the best point and shoot out there. Does it all. Sony RX100