My gaming PC cost me around €800-1000 seven years ago, then three years ago I got more RAM and a new GPU for around €350. I reckon I'll get another one or two years before I've to upgrade the GPU again, probably when Cyberpunk comes out, which will give me another 3-4 years. I'd say that's a pretty damn good investment for that money, considering I've generally used it way more than my PS4 and not just for gaming either.
Entering into the gaming market for a PC is more costly than a console for sure but works out pretty similar long term if you're not obsessed with having the new CPU, GPU etc. as soon as they come out. PC games aren't advancing nearly as much as they used to so you don't need to upgrade remotely as much.
Anyway, back to Google Stadia, I reckon it'll bomb big time, especially when MS and Sony release their new consoles for around 400 quid. We're still a good four or five years away from streaming being a viable option for gaming. And Google don't exactly have a good record of continuing to support failed projects.