Old cobalt glass is so pretty and can be quite collectible. Of course, that depends on what kind of glass you have. Cobalt blue Depression glass like Aurora or Royal Lace is very desirable so can command a high price. The most expensive pieces would be the rare ones like mixing bowls or refrigerator dishes. Small vintage cobalt blue vases can be found at thrift shops for next to nothing. So it depends on what you have.
There are many modern pieces of cobalt blue glassware as well as reproductions. You must first learn to identify what it is that you have before you can access the value. Find a helpful book on Depression Glassware to learn what you have.
If you mean that you have blue bottles (I love those cobalt blue medicine bottles, they are so pretty) here is a book that may help you:
"Cobalt Blue Glass Edition" by Schiffer Books was printed in 2001 so will not reflect current values but can help you identify your items.