COKOLISO

I am looking for an apartment in the other side of the tejo river...Almada, Seixal, COrroios, Barreiro, etc. Which are the best places to find an apartment safe and economical? I will appreciate any help.

moving shortly

You could try Alcochete. It is still up and coming, it has been proposed that the new airport may be built there. There is a big outlet shopping centre there. The crossing over the new bridge into Lisbon is within spitting distance which will take you to the present airport and Expo site. Every year in August Alcochete has a Sardine Festival. The main street is turned over to look more like a Wild West town with a bull in the street, twice a day a new bull is bought into the town, horses and the cows are run though to pick him up.

Its worth a visit to look.

Gosia

This is why I would not recommend Alcochete... Imagine, crowds, stench of sardines, bullfights - a barbarian festival.
Almada, Seixal and Barreiro have lots of poor areas where the appartments might be very cheap but you really would not like to live there! Crime, dirt, poverty.... Do not rent anything without seeing the place and the area first. Of course there are also nicer districts where you can find reasonably priced apartments.
In Corroios you can find houses to rent and they will be cheaper than on the otehr side of the river.
If you depend on public transport, you can look for an apartment in Almada (train from Pragal and boat from Cacilhas), Seixal (boat), Barreiro (boat), Montijo (bus to Expo and boat), you have to be careful which area to choose. Maybe Montijo and Corroios have a bit better reputation than the others....