Old post but still watching.
Speaking as someone who’s worked in both retail and retail tech for the last 15 years or so, what I see you want as as POS is:
1) definitely touchscreen.
3) reasonably priced.
Given that you can buy a brand new iPad for $379 or so and given how stable it is as a platform, how could any other option compete except for outlying use cases which Shopify isn’t designed for.
Retailers are really fond of having a POS system on desktop since it will guarantee a more consistent connection between online and offline platforms (as better Internet connection).
It's really unfortunate that Shopify POS hasn't support POS system on the PC. However, Shopify App store features lots of supportive POS software that are compatible with PC. You can check out ConnectPOS since the app is suitable for both PC (Windows & Mac OS) and mobile devices (iOS & Android). This will support the best performance for your store.
Hope this will help you.