Puerto Rico can be expensive, but in reality if you look a little it´s really much cheaper than the Mainland...let me explain...
First of all, where were you living in Ecuador? I´ve been to Guayaquil and all along the coast, and at least in Guaya I noticed a pretty good deal of Americanized businesses, lots of fast food, etc., at least way more than here in Colombia. Well Puerto Rico is full of Mainland chains also...it seems like on every interstate exit in any little pueblo the first thing you see is a Walgreen´s and a Burger King. A lot of Mainland low-income tastes and habits are the norm for everyone on the island...fast food, Rent a Center furniture places, payday loans, etc. Crap chains like Applebee´s can be all the rage for young people, I don´t get it really...but I guess it´s something different for them.
Take it for what it is, it´s part of the landscape. You have these options available to you, but if you dig deeper you will find that you can go cheaper than that. To really save money, get used to taking all out cash and utilizing the local/informal economy as much as possible. The plazas del mercado are more what we´re used to in South America, if you give yourself time you can find delicious fruits and veggies at a very cheap price. Often you´ll find trucks on the side of the road selling produce, and there are always cheap local places to eat at lunchtime, some on the side of the road and others are inside of bakeries and supermarkets...the portions are MASSIVE. Honestly there´s no reason for you to not save half for dinner and maybe add some veggies from home for more balance...meat and rice and beans are great, but you´ll notice the island has a big obesity problem...don´t fall into that trap, try to control those portions and add more colorful foods to your plate. The seafood is delicious, but to get fresh fillets and shellfish you often need to take a ride to the coastal towns...pork and chicken are much more commonly eaten.
Insurance in general is much cheaper. There is something call the
marbete for your car, which is the minimum coverage you need to legally drive there, provided by the government. I don´t remember how much it was, but it´s much cheaper than the Mainland...if you were wondering if you needed a car in Puerto Rico, the answer is a resounding YES. Maybe you could do without one in San Juan, but it still wouldn´t be fun. Medical care on the island is much cheaper than the US, but there´s going to be a lot more waiting and from what I hear there is quite the exodus of medical professionals, so I´m not sure if the savings are worth it in the end.
Where could you end up paying far more than the Mainland? Well your electric bill will cost an arm and a leg if you run the air conditioning for any period of time...get used to box fans and sweating a little. It really wasn´t a big deal for me after a while. Obviously things like appliances and some foods from the US are going to be more expensive, but I don´t think the differences in prices are out of this world.
This website is the best, it´s more trustworthy than Craigslist:
https://www.clasificadosonline.com/
As you can see, rent is cheap cheap in many places. I highly recommend landing somewhere on the West Coast. I loved living in San Germán, and I was tied to there because I went to grad school at Inter. Up and down that side of the coast though is all paradise. Cabo Rojo, Rincón, Aguadilla, Aguada, Isabela among others are all wonderful places.
I don´t think the average Puerto Rican has any sort of chip on their shoulder in regards to gringos, remember there are more Boricuas living Stateside than on the island itself. In the last 10-15 years the island has taken in more Mainlanders and become more diverse in terms of immigration. Your Spanish level will very much dictate how your experience goes I guess. I got to Puerto Rico in 2011 with basically nothing, my Spanish sucked. I stuck with it and after several months there I starting moving towards an intermediate level, but I quickly hit a wall. Why? Well trying to "make you feel comfortable" many Puerto Ricans will just answer gringos in English if they hear any sort of accent whatsoever or if said gringo doesn´t flow in a native way. Sometimes it seemed like a passive-aggressive intentional snubbing, especially in the Metro Area, but other times you can tell people are just thinking they´re being polite. Since I´ve been living in Colombia I´m at the advanced level now and I lost my gringo accent...well I went back to visit last year and voila, no one answers me in English anymore. Either way you´ll be good, but to really feel most accepted by the locals you´ll have to come with it in terms of your Spanish fluency.
Let me know if you have any more questions...I still have some of the kindest, warmest friends in the world living on that little island. Sometimes I wish I could live there again.