Space, not cost.
120GB minimum. People always say 'just Windows' for a new SSD.
It never ends up as being 'just Windows'.
Sure, you could install it on a 32GB drive. But you will spend far too much time in fooling around with it, for very little gain.
120GB drive minimum. If you can't afford a 120GB or larger, don't bother.
Samsung 840 EVO.