Looking for some ideas for hotels (or hostels with private rooms) that are more on the affordable side (say around $100 a night, around the Baxia-Chiado area in Lisbon (Portugal).

Also suggestions for Porto and Sintra area as well (as I will be spending 2 days in Porto and would like to spend a day in Sintra.)

Doing a solo trip in mid/late September time frame so during the shoulder season. I don't need anything luxurious as long as it's clean, in a safe area and reasonably quiet and near public transportation (bus/tram) as I will not be renting a car and will rely on public transportation.

(I'm OK with hostels as long as I have my own private room that I can lock -- OK with a shared bathroom arrangement.) This will be a solo trip as well so can do with very basic amenities, as I'd rather spend my money on tours and food/experiences, and less on hotel/hostel stays--I'm not that picky except for having my own room to myself. Other amentities like breakfast and wifi are not as big of a deal.)

Use booking.com for your accommodation research , you'll find several that meet your budget criteria.
I would call them directly to make sure the room is private ( instead of shared) before booking.
At that price point, in that area in September expect very basic accomodation.
Lisbon has a good Metro system, you may want to consider other locations that have Metro access if they meet your criteria.

Hi!

Cannot help with Lisbon, but I leave a suggestion for Porto: Vivacity rooms and apartments. The rooms are very good, and the price for the rooms includes breakfast (with natural orange juice - Mr. Joaquim, the owner, has a farm with lot's of orange trees), and the location is great (uphill, two steps from the art neighborhood, the House of Materials, Carmo and Carmelitas churches, Clérigos tower, among other things). It's a family run business, which I think it's nice for someone travelling solo.

Hi,
Here are some sugestions which could meet your target price :
Lisbon
These accomadations are not located in the Baxia-Chiado area but in close neighboorhoods :
easyHotel Lisbon
Amor Lisboa Hostel
Lisbon Wine House
Porto
Pedra Iberica
HaoBo Porto Center
Lusitana Hotel
Sintra
Casa do Albuquerque
Chalet Saudade

Have a nice trip in Portugal !

Here are some affordable places to stay in Lisbon, Porto, and Sintra that fit your criteria:

Lisbon:

In the Baixa-Chiado area:
Hotel Internacional Design is a great budget-friendly option in a central location. Private rooms start at around $70 a night and include wifi. It has a mix of dorms and private rooms, so be sure to book a private one. It also gets very good reviews for cleanliness and location.

Lisbon Lounge Hostel a hostel with private rooms starting at around $80 a night. It's in a great location close to the city center and has a rooftop terrace with amazing views. They also offer walking tours and other activities for guests.

In other areas well-connected by public transport:

Casa Internacional is a hostel with private rooms starting at around $50 a night. It's in a safe and quiet neighborhood, and close to a metro station. Breakfast is included and they also have a communal kitchen.

If you're going to rent a car, then go for the outskirts of Lisbon, it has lower prices (less demand), and the highways / roads throughout the Lisbon district (which includes Sintra) are good.
A5 will get you anywhere between Cascais and the city of Lisbon, and IC19 will get you anywhere between Sintra and the city of Lisbon. Off-peak hours you can make the cross in well under 1h.
By the way, there's an inner road between Sintra and Cascais, and considering the size of both Sintra, and Cascais, I'd visit both in the same time.

If you're planning to go to the Pena Palace, make sure to buy your tickets well ahead of time as the tickets will be associated with a specific day and hour.