You don't have to buy new necessarily to upgrade. Only the newest (and sometimes overpriced) stuff requires 10, ie the current-gen Intel and AMD's new Ryzen.
If you want to get down and dirty there are "Swap" sites such as reddit's /r/hardwareswap or other forums where people are dishing out previous gen parts daily where you can snatch up some decent deals on cpu/mobo/ram.
W10 isn't all bad though, the biggest gripe is probably the random updates that are applied.