This is right, I participated in the public beta of Windows 8 on a Windows Vista machine.If memory serves from when I upgraded a few years ago, you can upgrade to Windows 8 from Vista. Then you could upgrade from that to Windows 10 provided there free upgrade still works. They officially ended the free upgrade a couple of years ago, but the last times I've tried it, the free upgrade still seems to work.
https://www.ebay.com/itm/Microsoft-Windows-8-Pro-License-Only-1-PC-s-Upgrade-for-Windows-3UR-00001/254156027112?epid=177514521&hash=item3b2ce134e8:g:w90AAOSw2bFcEGvV&LH_BIN=1
Those I think sold for 40 bucks new in 2012. So if that's legit, that's probably about the cheapest legal path from Vista to 10.