The cheapest plan is 1 GB for 7 days at $1.29. That is the right starting point for a lot of travelers. If you mostly use maps to get around Stockholm, check messages, and look things up, 1 GB over a week is often enough.
Spend a little more and you get a lot more room. The 3 GB plan for 15 days costs $2.10. The 3 GB plan for 30 days is $2.24. For most week long trips, one of these two is the sweet spot. You get breathing room for photos and a bit of browsing without paying for data you will never touch.