Want to buy cubase pro 9.5

I have cubaseai8-cubaseai10 and I would like to upgrade to cubase pro 9 or cubase pro 9.5 , whichever is affordable right now…does anyone know where or how I can buy a download for this?

Only the latest version is available to buy, but that license is also valid for earlier versions of the same product.

You mean I cannot buy an earlier version of cubase pro and then after time, gradually upgrade $129- 299 or so each upgrade until I reach cubase pro10?.They seem to be selling older version third party(on the internet).

I have no idea what third-parties sell. Steinberg provides a way for people to sell their license, just make sure your seller follows that. Google Steinberg Resale Wizard to learn about that.