It really isn't about what you can afford, it's about what you can do. If you're on a laptop with an SSD, you have 128GTB, maybe 256GB if it's a new one.
You can get 960 GB and 1 TB SSDs for 2.5", even for mSATA (480 GB, but you can place 2 of them)
Don't talk to me about price though, doubles the value of the laptop ;-)