I've never heard of valuation required for postal service. I state the amount I want to cover, and that is priced commensurately. Are you using US Postal Service or someone else?
For example, I shipped a 2000s Seamaster Professional using Priority Mail to Seattle and insured it for $2500, which is about replacement cost.
For you, I would recommend registered mail and insure for $5000. It will cost a
lot but it's worth it.
For registed mail, btw, you must use paper tape to seal the box, as they stamp it all over to detect tampering.