Guinness 0% is the only alchohol free thing that I've found to actually taste like it's original counterpart. Most places seem to have it these days.

Avoiding sugar is going to be difficult as it's the default for non alcoholic drinks. As others have said lime (or other mixer) and soda is probably the best bet.

To add insult to injury I'm finding that a lot of the non alcoholic options tend to be priced higher too.