It seems to vary a lot by state (USA). For Florida, a single
member LLC was cheap and easy (few hundred bucks
including a one year LegalZoom subscription, annual
maintenance under $200). I also reside in an unincorporated
area, so no city bureaucracy with its hand out for doing
you the favor of not shutting you down.
But other (esp. Up East and California) locales you can
bet on more "up in your business" governmental license,
form, fee etc.
Since things are very localized advice from Internet randos
is probably not going to get you as far as local small biz
resources.