Between Sept. 15-30, with a two-night stay, you can get an 85 euro rate at 12 different pousadas:

Alcacer do Sal, Arraiolos, Beja, Estremoz, Marvao, Manteigas, Torreira, Viseu,
Queluz, Ourem, Palmela, Alijo.

Though these may not be the most popular pousadas, some of them are really nice. Alcacer is very modern in the walls of an old castle, nice little town, near salt flats;

Arraiolos -- several of us routinely rave about that one, in an old convent surrounded by countryside

Beja -- old monastery in a southern Alentejo town that is a good base for visiting that part of the Alentejo

Marvao (haven't ever stayed in the pousada but it's a gorgeous little town);

Manteigas (don't know it);

Torreira (nice on the inlet, very peaceful, though not much in the way of architecture);

Viseu (one of the newer pousadas, done in modern minimalist style, not my ides of how to decorate a 19th century building);

Queluz (recently totally renovated, very close to Lisbon, near the Palace of Queluz which is an often overlooked gem IMO, also well situated for driving to Sintra);

Ourem (never been there),

Palmela (castle high on a hill, very nice and close to Lisbon);

Alijo (modern and comfortable but not a jaw-dropping place -- in the Douro Valley but relatively far from the river).

This is a good price for room and breakfast for two.

Website: http://www.pousadas.pt/historic-hotels-portugal/en/promotions/saldos-verao