What I understand of a 3000 hr life extension inspection;
The original manufacturer (or later the type certificate holder) has set forth a specific set of inspections which are more comprehensive than an annual inspection of airworthiness.
Sometimes some components are identified as mandatory replacement items.
Sometimes access holes have to be cut to inspect otherwise inaccessible parts, then these holes are patched.
Some makers charge a fee for serial number specific documents, some makers require this work to be done at their facility or repair station.
Your experience may differ. It doesn't sound inexpensive to me.
Good luck!
Scott