There are lots of achievements assets on the store, you only looked for xbox.
These are kind of like it, but not official, and a lot cheaper.
https://www.assetstore.unity3d.com/en/?stay#!/content/4110and
https://www.assetstore.unity3d.com/en/?stay#!/content/3042If the other asset is too expensive, you don't need to be looking at xbox builds yet. Renting the license for xbox will be more expensive than that asset.
The packages above let you make your own system for achievements, leaderboards, etc. The bonus is that it isn't locked into Xbox, Google, or Apple. It will be your achievement ecosystem that goes anywhere you build for, and since you would be starting with this, You can stick with the same database that's branded to your studio your whole game dev career.
And even though its playmaker, there is still code involved. Every one of these actions is a snippet of code. FSMs get built into the game with other code. But it is still code.
If you want to build a generic achievement system solely with playmaker, I see no reason this wouldn't be possible with supplied actions, ecosystem, maybe some custom actions, but off the top of my head, I don't think any customs would be needed for a basic setup. But you could use playmaker to learn enough C# to extend everything.
So... Grab assets, or start playing around with FSMs and get to work. Break stuff, fix stuff, repeat. You'll get the hang of it