Being an NFA dealer in Washington is a possibility, but it does cost a lot of money. If you don't have an actual retail location, it will be very hard (but not impossible) to get the required licenses from both ATF and the state. If your plan is to go this route strictly to get NFA items, be mindful that ATF WILL bust you eventually and charge you with tax evasion! It has been done. If you are actively involved in doing LE and MIL demos, and buying and selling stuff, you won't have a problem.
Lots of info here:
www.atf.gov/firearms/nlc/index.htmAnyway, here are the base costs:
NFA Dealer (not a manufacturer or importer.)
Type 1 or 2 FFL - $200/3 years
SOT - $500/year
State Dealer license - $125/year
State Business license - $15 (one time)
City busines license - $55/year (for Renton, other cities may/will vary)
$762/year in Fees. This is before you sell a single item, and does not include rent for a retail location. Once you have retail sales, you get to tack on B&O taxes (once you exceed the small business deduction threshold that is.)
NFA Dealer & Manufacturer (as well as importer.)
Same as above, but add the following:
$150/3 years - Type 7 Manufacturer license
$1,750/year ITAR fee.
$2,562/year in fees.