Genuine Baltic amber is more than 45 million years old and the mining process takes several days. Prices begin around £5 and can be as much as £30 for 1 amber teething bracelet. In general, the more rounded the beads, the higher the price of the bracelet.
If a bracelet is for sale at a discount, question the vendor about its authenticity. Many of the lower cost bracelets are just glass or plastic and will do nothing to alleviate your baby's pain. (If a Baltic amber product says Made in China, it's probably fake. They don't have Baltic amber in China. Of course they can import it, but mostly, they don't.)