For visitors to Portland, the cheapest way to arrive and leave from PDX (Portland International Airport) is via the MAX light rail system. There are four color-coded lines: Blue, Red, Yellow and Green.

MAX connects the airport with downtown Portland;  the west side silicon forest area of Hillsboro;  the eastside suburb of Gresham;  Delta Park and Expo Center to the north;  plus the southwest suburb of Clackamas, including the big shopping mall.  

Trains run every 15 minutes for most of the day.  Trains may be less frequent in the late evenings.

The ticket price varies, but currently tops out at $2.50 for a two-hour adult ticket to $5.00 for an adult *all zone* one-day pass. Fares.

Once in Portland, MAX is a great way to get around without a car.

There is a current special with Radio Cab from downtown Portland to PDX for $26 or from PDX for $28.50 for a cab.  This is a good deal for a flat rate cab vs using a shuttle.