Max! My question for you is: Do you need to get to Astoria in a day? And are you set on de-training at Kelso? (Okay, I asked two questions, so sue me.)
If you were coming down from the north, you could get off at Centralia, WA and then ride out using SR 6 to the coast and pick up 101 at Raymond. SR 6 has some rolling hills but is a relatively easy and pretty quiet way to get out to the coast. This routing would of course be longer at about 110 miles, so it would be a two day ride. Here is the rough route:https://maps.google.com/maps?saddr=Centralia+Amtrak,+Centralia,+WA+98531+(Centralia+Amtrak)&daddr=Astoria,+OR&hl=en&sll=46.71747,-122.953062&sspn=0.006341,0.013797&geocode=FR7ayAIdmuKr-Cnxe4bAKl6RVDEI8cTGuFEV1A%3BFWzFwAIdK3ye-CmL-5UJRHuTVDG_ihuh8XLd9w&oq=astor&dirflg=b&mra=ls&t=m&z=9&lci=bike
(Note: Google Maps routes you on the "Willapa Hills Trail". Much of this trail is not improved and there are lots of washed-out or unrideable bridges and rough surfaces. Best to stick to SR 6.)
You could camp at Bruceport County Park outside of South Bend, which would be about 70 miles from Centralia.
If coming from the south, you can get off at Portland and take "Route One" from this link out to Astoria:http://www.portlandoregon.gov/transportation/article/301633
Also about 100 miles, but can be broken into two days.
If you do want to get out to Astoria in a day, and want to de-train at Kelso, I'd probably go with option one that you listed as it's the fastest. All of those options use high-traffic roads that sometimes lack shoulders, and you will be hitting a few good hills that you really can't avoid. I despise the Lewis and Clark Bridge, but others find it less odious. Option two might be the least hilly, though.