Lisbon and Porto are super popular with ["digital nomad"] remote workers who work for international companies so earn in USD but spend [much less] in Euros for a superb lifestyle.
There's a reason @paddycosgrave moved Web Summit to Lisbon. It's one of the cheapest cities in Europe and [unlike Barcelona] everyone speaks English. There is a good "tech scene" and a fantastic work-life-balance; surf, great food & warm/welcoming people.
A few things to consider that many people over-look: + Socio-Economic and Political stability. + General safety/security and crime levels. + Sanitation and healthcare availability/cost. + Availability/cost of healthy [organic/unprocessed] food. + Lifestyle to actually live in the place: is it "cheap" but a nightmare to live there? + Contract-law for short-term apartment/room rentals.
Portugal will exceed your expectations on all of these.
Portugal is very welcoming to US citizens, you won't have any "visa issues" the way you will in many of the [superficially] "cheaper" Asian countries.
If you want your budget to stretch much further, consider Braga. The cost of living is less than a third of SF, internet is fast and you get most of the benefits of Porto & Lisbon (or can reach those cities with a short train journey).
Note: I am [slightly] "biased", my Wife and I have recently "escaped" from London [after working there in tech for 10 years] and we are busy setting up a Co-living/Co-working House in Braga: https://github.com/dwyl/home We will be opening at the end of this month and our target cost per month [1Gbps Internet, all bills, cleaning & gym included] is $300 (USD).
We chose Braga because it has all the "ingredients" for an awesome place for tech/creative people to escape the bigger cities and focus on their work while still having access to all the amenities great healthcare, superb organic/vegan food and good libraries/meetups/etc.