Yes, I'll Grant you that if you've designed an interactive, multipage form then it is costly to rebuild it to degrade. However, I'd argue that the form was probably unnecessary technically complex and that starting with having a degraded option in the first place isn't additionally costly (and better protects the agency from ada lawsuits).

In the very rare cases that we're talking about a true webapp (i.e. Google docs, or I'll even Grant you GIS (mapping)visualizations, even if it's possible to degrade those), then yes, decisions need to be made on what minimal technical requirements are required. E.g. a government agency offering an application that only works in chrome would be a non starter.