2 weeks ago I almost did the unthinkable, hit a cyclist while driving a car! It was dark, in a badly lit neighborhood, I was turning right after a mandatory stop and out of nowhere a guy on a single speed passed me on my right. Thankfully I hit the brakes pretty fast and the rider was in no danger.
You have to determine what you need. You want to be seen or you want to see is one factor to consider when you start shopping. If you live in the city and most streets are well lit, you want to be seen. In this case you can get yourself a white LED blinker for the front and a red LED blinker for the back of your bike. Blinking lights grab attention and that's what you want in an urban setting full of distractions. These range anywhere between $3 to $25. Over $10 I think you are paying too much. You can also think outside the box and go shop elsewhere for blinking LED's. The bike pictured in this post had it's vintage headlight refit with a $1 book reading LED light from the dollar store.