Coming out of Spring/Summer and into Fall, Bubblegum and Graduated bead necklaces are still fun and fresh and give a great contrast to button down shirts and trousers. These necklaces are available very inexpensively. These two are from Target. The first is made of wooden beads and the second is made of plastic beads. They are each around $8 at Target. If you don't want to see the same necklace on everyone but you want to be on trend, there are equally inexpensive vintage options too.
But if you are looking for some totally unique options, visit Etsy.com. The artists there have created some amazing pieces, including this garnet and brass necklace that looks like bubbles or a Deco graphic. You will definitely be the only girl at the party wearing this one. And it's only $30.
So whether you want a trendy look or eclectic and unique (or both) there are some great options out there in totally accessible prices.