The law here does not necessarily mandate 'UL' per se, (most panel builders still use UL) you can also use international standards like IEC or CSA, it does have to be built to a recognized standard and a 3rd party needs to say its safe.
for a complex panel use ETL is going to be way less expensive than UL and they have an office in Portland.
Oregon requires electrical products (including your panel) to be 'certified', depending on what it is and how complicated you might be able to work directly with your AHJ and or a state inspector and have them certify it.
To do this it needs to be real simple and you'll need a copy of whatever standard(s) you use like UL 508A and provide a copy to the AHJ.
I have done it this way a few times when I had to re-do a control panel or expand one.
It is entirely up to the AHJ, you should also look into the master permit program if your not already in it.