Yeah even now i have allocated 100 gb alone for c drive and only 60-70% space is utilized.Sorry, just checked. Then any cheaper SSD would do, I guess.
I have this thought just now. With 120 gb, the useable space would be around 100 gb. No idea how much windows installation and other software installations, headroom for downloads etc would take and also make sure the SSD is at least 25% free all the time to avoid slow down. Hopefully, 120 gb is sufficient.