The census matters a lot for representation, which in turn effects elections. It also matters for funding things such as transportation and social services. One huge difference between the US and Norway, besides the points mentioned above, is the number of undocumented residents in the US. The only way to count and provide for them is to manually count, because they're um, unregistered. Sadly, they're also afraid of being deported, so are far less likely to respond. There's also typically a lot of fear mongering that swirls up whenever the census is conducted.
To your point about technology: This is the first time the census will be completed online. The problem is multi-faceted. It increases the fear of discovery and deportation, it requires resources undocumented workers and the working poor may have little or no access to, and these workers tend to live unconventionally in converted garages, or sharing housing with multiple families, or as was recently discovered in NYC, in housing that doesn't legally exist. The census worker's job will be to track down the people who fear the process, or due to language barriers, don't even know it's going on. Then there's the whole anti-gubmint crowd who aren't going to want to be counted for a host of other reasons.
Unemployment on the US is at near-record lows. They have to pay a decent wage to attract enough workers to get the job done. They also need workers fluent in many different languages. I wonder how many languages the census is conducted in in Norway? Yeah, there's a whole other layer of costs to consider.
It won't be easy, but it's vital. It costs what it costs, because it's a Herculean task. Comparing the US to anyone else's cost to collect accurate census data is rather pointless.