You can also keep the hard drive and replace the optical drive using several brackets available on the market.
Depending on which MBP you have, you may even be able to fit a 12.5mm SATA drive, which means you could potentially squeeze in a 1TB drive.
I've heard Apple's SSD drives are expensive and there are better options, like http://eshop.macsales.com/shop/internal_storage/Mercury_Extr...