Fact is - most people don't realize they dont need a huge size. Put JUST the OS on it and put all the programs/etc on a 7200 RPM drive (if laptop - whatever speed you can decently get that doesn't suck your battery dry as a ... (well leave off the analogy).
Bottom line, most people will and should afford enough of an SSD for their basic OS. Put the absolute necessary on it, and put all user info/data/programs you dont need/use every day on different drive. It's easier in Windows 7/Vista but Microsoft is still screwed up in their head thinking people don't want their user data separate from their OS. God when will they get a fricken clue that it is a GOOD thing to have OS separate from USER data for backups/reinstalls/restores/etc? 20-30 years and they havent figured it out. As just one example I do this because the OS drive slowly gets bogged down with crap. I pull out my trusted backup that has most apps I use on it, install it, and boom ready to go again. If I have major installs - I load it anyway, do the installs, and save that back up. Makes life so much easier not living with Microsoft's seemingly planned obsolescence of your OS install.
Regardless, less than 100GB will do, in fact 60GB will prob do for the basic OS install and the one or two MUST have apps that need to be fast as hell on your PC. I realize it varies for each person, and this is a general example, but people can afford these great productivity improvers if they just keep their OS separate from the rest of their crap. Microsoft doesn't make this easy - thats for damn sure. It is the one major update to Windows I would pay an extra $50 for - to completely BE ABLE to separate Programs from OS from Personal Data/Settings. It means I could walk up to any trusted PC -hook up a dual SATA dock or USB 3, and start using the system with my set of programs and my set of data/settings.