Unfortunately, I have no prices available - I only remember 50g candy bars costing around 15-20 NOK. Generally, Norway is pretty expensive, they tax all the fun, especially meat and sugar. However, shipping to Norway is also expensive.
I wanted to have a lot of salami snacks and protein bars (like ~1kg of each for 200km) . Thus, for me, the shipping costs for a package every 200-300 km did definitely amortize well. If you have a modest candy consumption, things may be different, so I don't want to give you advice in this case.
None of my package stations charged a fee, but in all cases I spent a night there. I feel, the STF stations would not care if you pick up your package without using any of their servies. (Generally, people in northern Scandivia are very helpful.) Shipping to a post office may also be an interesting alternative. I did not try out. Please report, if it works for you
Food in Sweden is cheaper than in Norway, and so is shipping to Sweden. In paricular, Gäddede and Storlien are interesting alternatives in this regard.
Staloluokta's kiosk accepts banking cards. Unna Allakas and Abiskojaure do not! In small villages, card payment is generally possible, in Scandinavia this is pretty common.