The long haul trucker is no longer made, and all bikes a re scarce right now. If you want a Disc Trucker you might be able to find one, but you better start looking soon. As bike friendly as Portland is, I would not count on finding one when you arrive in PDX.
You can ride from the airport to the train station, where you can catch the Amtrak bus to Astoria. We have taken the bus to Astoria from Portland and also done the trip in reverse. We usually ride to the train station in Albany, OR and take the train to Portland and continue on the train to our tour start. If we are flying we pack our bikes and figure out how to get them to Portland. When the cost of car rentals was reasonable it as not a problem. I needed to get four bike boxes to Portland Airport, and rented a 4-door full-sized pickup for less than $100 for the day.
Starting in Florence is a bit more of a challenge. There is a train going to Eugene, but getting from there to the coast could be iffy. I'd check on the availability of a rental car that could be returned in the Florence area.
My wife and I have flown or taken the train back from tours landing at PDX or taken the Empire Builder train to Portland.
I think the best option is to take the bus to Astoria from the Amtak station in Portland. Depending on your arrival time by air or ground,you may have to spend the night in Portland to meet the bus schedule.
Good luck!