Since the Washington Governer got involved in on line gun sales to collect tax you should only be taxed when buying from a business not a private seller. You can buy from private sellers on GunBroker as well as FFL holders/dealers. The FFL I use only adds WST on incoming firearms from a business and never from a private seller.
Example: If you and A private seller go to a FFL per the fantastic new I-594 law and transfer a gun you bought from him or her do you pay tax when doing the transfer? No, you don't or shouldn't, you only pay the transfer fee. Same goes for a sale from any private party regardless of where they reside or where it was shipped from.
If you have the patience and aren't in a hurry you can find very good under market deals on GunBroker. Not so much on GunsAmerica or GunAuction.com, both of those sites in my experience tend to have higher prices.
Good luck!
TV
What FFL transfer guy do you use?
To the original poster, buying online can save you cash. Every year I buy guns from out of State and have them shipped here to JC's Pawn Shop up in Mt. Vernon to do the transfer. They always charge the BS Washington State "Use Tax".
A couple of years ago I bought a new Sig Saur Mosquito from Piazza Jewlery & Pawn out of Missouri, With the shipping, transfer fee and the "Use Tax it was cheaper then Cabelas base price for the same gun, so searching around can save you money on your purchase.
I buy older 22 rifles and older 410 shotguns, many from out of State, I got a C&R Permit, I buy these guns, send them a copy of my Permit and get them shipped directly to me at the house. It is a Class 3 FFL License, so no transfer needed, My first purchase paid for the $30 - 3 year permit.
These Permits are good for guns over 50 years old, Military Guns and Commemorative Guns.
I'll be picking up a 22 Handgun locally in a week or two with my C&R Permit, non NICS Check, just finish paying it off, give them a signed copy of my Permit and go home with it.
Check out ArmsList in different States for the gun you are looking for, I've found some good deals looking else where. Some times you can make an offer and get it at for lees the advertised.
By the way, nice choice of rifles.