When I first saw this post a scripture came to mind (reply #2 was in this context also)... "the labourer is worthy of his hire" (St. Luke 10:7). In First Timothy 5:18 we read "For the scripture saith: Thou shalt not muzzle the ox that treadeth out the corn: and, The labourer is worthy of his reward". I am also thinking the verse may be found in the Book of Proverbs but I don't have time to search that out.
In order to get an internet signal to a local router or a port on your computer (whether by DSL phone line, fiber optics cable, or satellite ... though to mention the latter may be politically incorrect here as apparently some do not believe in satellites), someone or several have had to invest their capital for equipment and their labor for the manufacture and installation.
Public libraries and school libraries offer no fee internet, paid for by the tax structure that supports them. Libraries usually offer a comfortable research and study environment, sometimes one can even reserve a private study room. The disadvantage is that one is limited to the hours they are open. At the rural library branch near where I live (only open 15 hours a week) people will come and sit in their cars to access the free signal on their laptops or phones when the library isn't open.
internet cafes and some coffee shops offer free internet, though usually with the expectation that you will buy some food or beverage item. Again, one is limited to their open hours, and the environment may not be as calm and quiet as a library's.
Some apartment complexes may offer "free" wi-fi in their amenities package. It's not really "free" of course, its included in the rent, but may be a lesser cost option than paying for a separate internet service. A potential disadvantage may be that unless the building owner put in a system with adequate capacity it may be very slow in the evening when everybody in the building signs on, especially if they are streaming movies.
You mentioned "paying the neighbor", and this could be a good option if you get along well. Offer to pay a portion of their internet cost and they will share their user ID and password with you. You both save money.
An option that I have used in the past when I needed to be frugal: A few years ago I didn't want to pay for an in home cable internet connection (it would have been $50 - $60 a month plus connection fee, router lease, taxes, and etc., etc., etc.) I organized myself to do most of my internet activities (sending e-mail, downloads, research) at the library when it was open. Routine functions such as checking e-mail I could do on my mobile phone. I don't like to type on my phone so e-mail replies (or forum posts) would be saved for my next trip to the library. Another advantage was that the library was always warm and cozy during the winter so when I went there I could turn the apartment thermostat WAY down and save money on heating.
Unless one has the most basic / cheapest cell phone plan, most plans will have a mobile hotspot feature where the phone's data signal can be shared with a computer via usb cable or bluetooth. There may be limits or extra costs. I found at the time that by primarily using the library to access the internet with my laptop (most libraries also have computers one can use), using my mobile phone for simple routine functions, and using the phone's mobile hotspot feature when necessary (and only then), I saved a bunch of money.