Freeport Outlet is closer to Lisbon than from Setúbal. To get there you can take a bus or rent a car. You can take the bus 413 from Setúbal bus station or the 431, 432 or 437 in Lisbon (in Campo Grande station - north part of Lisbon or in Gare do Oriente - Eastern Part of Lisbon). Schedules can be seen in http://www.tsuldotejo.pt/ choose lines in the menu and then lines-suburban.
Knowing you don't have your own transport, the most practical and economical way to get to Alcochete is by bus which undoubtedly makes it one that's a highly scenic ride out of Lisbon.
There are two buses - numbers 432 and 435 - both serviced by the TST Bus Company. It departs from the ultra modern Oriente station, an architectural marvel by Santiago Calatrava and the bus zips thru the breathtaking Vasco da Gama bridge an equally awesome architectural structure also by Calatrava. It's two stops and one is safely deposited at Alcochete. The ride itself takes less than an hour.
And one picks up the return ride to Lisbon from the same drop off place in Alcochete.
From Lisbon you can get to Alcochete using the services of the bus company Transportes Sul do Tejo, from Oriente metro station/bus terminal. However, I didn't use this company as I was driven around, but see Jorgec25's Alcochete page for more detailed information.
Coming from Lisbon, you can easily reach Alcochete using the TST (Transportes Sul do Tejo) Buses.
Just go to the Bus Terminal at Oriente Station. You can reach the station using the subway – last stop on the red line. If you are coming from the airport just take a taxi or the airport express Bus and it’s a ten minute ride.
At the Bus Terminal go to the Place 27C, to catch a TST Bus. You can use the Number 431 (the most frequent), but also 432 and 437.
All of the above Buses stop right in the centre of Alcochete, next to the Main Church. You can also catch any of theses Buses to visit the Freeport Outlet.