It's actually two swap meets in one, the original and largest is at the Portland Expo Center and runs April 1st, 2nd and 3rd. The second swap meet is next door at the Portland International Raceway, and though it is the smaller of the two, it's still a huge swap meet in it's own right. The PIR swap meet runs March 31 through April 3rd.
You can easily spend three days walking through both of these swap meets and not see everything. I've been going to this swap meet for almost 30 years now, and I still enjoy it.
Hotels near the Expo Center are probably already booked, but hotels in Vancouver or Downtown Portland always have vacancy. There is off site parking with free shuttle buses to take you to the swap meets, take exit 306B from I5 and look for the parking signs.
