Suzy: Extensions can be very expensive, and if not done properly, will not last- might as well throw that money out the window!
Make sure you're dealing with a reputable salon- remember, you only get what you pay for. Ask lots of questions about how long they will last, any special care needed, and what you can do to make them look their best.
I know in Miami the best place to get them is d r bonlie salons in Key Biscayne and North Miami. Check out his site at http://www.drbonliesalons.com
100% human hair extensions that can instantly (a few hours) from chin length to below the bra strap. The downside to using hair extensions for instant long hair is that hair extensions are not inexpensive and human hair is the most costly of the add-on hair options.