If you're looking for a slightly cheaper alternative, t + j Designs has some eye-catching neon necklaces that might be just what you've been craving. These beauties range from $38-$40, and they have other sparkle for even less.
Another option comes from fashion-blogger-favorite Spike the Punch. I was late to the Spike the Punch lovefest and now it seems most styles are out of stock, but I'm sure they will replenish their neon necklaces eventually. Most are $50.
Finally, I picked up a clear crystal necklace from Forever 21 a few months ago now and plan on painting it (eventually) with neon nail polish, so there's always the DIY route.
If you've found a great neon necklace on a budget, let us know in the comments!