I tried the thin-client thing and there are definitely pros and cons. Second hand thin clients are indeed often cheaper, have more ports, are upgradable. Howev

I tried the thin-client thing and there are definitely pros and cons. Second hand thin clients are indeed often cheaper, have more ports, are upgradable. However, if you're buying a $5 computer off ebay, you can't always find everything you want, and you might find that the hardware isn't ideal for what you're doing. The nice thing about a raspberry pi is you know exactly what hardware you're going to get, what dimensions its going to have, etc, at a reasonable price point. (Another advantage: when it breaks, you can get a drop-in replacement).