Mechanical disks are basically free in this day and age, so that's still a pretty significant savings over an SSD which is more like the price of a mechanical disk 10 years ago. You could cheap out and do a small SSD/large HDD combination, but I find that having an excessively small system drive is nothing but headaches, especially for software development where you are frequently installing different toolchains, etc. Until I can afford an SSD that is comfortably in excess of my storage requirements, then I'll stick with the HDD.