For plywood and shelving as a beginner, a saw in the mid-price range is totally fine - around 80 to 150 euros. Makita and DeWalt are solid options there, they really last and have good ergonomics. With the cheap versions, the problem isn't so much the upfront cost but that the motors wear out quick if you're using them regularly. Plus: cheap saws vibrate more, which is annoying when you're cutting larger boards and messes with the cut quality.
What you should specifically look out for: at least 1200 watts motor power, a good base plate (it has to be stable and adjustable) and decent safety features. Lots of beginners underestimate how important a good guide rail is - if you want to pay attention to straight cuts, a parallel guide as an accessory is worth it. For the plywood itself, I'd recommend a blade with lots of small teeth (at least 40 teeth), otherwise the material will tear out at the edges.
One more tip: maybe borrow a used one from a friend or from a tool-sharing project before you buy. That way you'll quickly figure out if the size feels right and how it handles - makes more difference than you'd think.