There are many SSD options for under $100.. Although you'll be getting less than 100gig of storage space. If your main concern is abundance of storage, hybrid hard drives (HHDD) are an option; they combine massive storage with near SSD speed for considerably less. There are several options around $100.
I've been contemplating replacing one of my drives in my Asus gaming laptop with a HHDD. I have dual 250gig's and one has recently become noisy..