[ninefathom]

Any of the late 90s / early 00s RISC platforms would be good for this. You could easily grab an AlphaStation, Sun Ultra, or pre-G3 PowerBook for such a purpose, and within your price range. Perfectly adequate for most non-browser tasks, and fun to learn if you're coming from the PC world.

Even the G3-G5 PowerMacs aren't really usable for modern web browsing anymore. The vanilla FOSS browsers aren't reliably building on them anymore, and even the "keep it usable" browser projects like TenFourFox are just barely scraping by performance wise on modern sites.

Note that your distro choices will be limited with these, but they all have at least a couple still available.