PawnDave-
If you know the earnings of the senior inspectors or fairly close, I'd start negotiations at 95-100%. I'd hold that position strongly as they sputter and back peddle and try to determine how bad they need you or someone else in the position which they'll display by their offer. Do the arithmetic between their offer, your bid and any other paid positions. They'll come up to meet you close if they really need you or someone and you're a known quantity so you actually are holding the good cards. Remember: your job well done saves them money already. At a certain point in your career they DO owe you a good living- you've put in your dues and proven yourself now it's their time to pay for the free ride they've gotten so far. You're not some rookie with an attitude. Show Me The Money!
Reminds me of an interview where the PM was tying to sell me a job about 15% under going non union wage rates. He knew I wasn't going to budge and they needed a sanitary tube welder badly. In frustration he sent me up to The Boss- actually owned the company. Bid Guy, like 325# [I'm a middle weight]. I size the guy up as someone who wanted to enjoy his success, play golf and smoke good cigars. We go over my resume which by then already had some credentials he was never going to see from any other candidate they were going to talk to. The guy was a salesman, like all his PMs, with a product that literally cornered the PNW market. He liked sitting in the catbird seat with a 300+% markup. Who Wouldn't? After making nice for a little while and then dancing around the money branch he was ready to put the cards on the table and asked me "What do you like"? I told him straight out, "I like skinny women and fat pay checks". He just rolled back in his plush leather chair and roared with laughter and said "Ok. You got it". Lot of guys in power aren't used to underlings talking straight and true and some of them miss that simple pleasure.
BTW. I know for a fact that WSDOT as of a year or so ago was down to 1 or 2 at the most, CWIs. Inspectors doing my inspections were expected t sit for the test but most were closer to retirement than it made sense for them to do. Might look into the starting package there for consideration. His name escapes me at the moment but the head of the Inspection Division is a pretty decent guy to work with as a small subcontractor and who would make the decision I'd guess. You could find out more on their website.
Best of luck