Most reliable is to buy mobile data service from one of the telephone companies. If you don't need to move a lot of data, the cost might be as little as $1 per day. If you move a lot of data, it can be much higher.
Looking at your budget in your greeting post, you be best off to find the places where Internet access via public WiFi is free. I don't mean coffee bars and restaurants where "free" means "for our paying customers" because you likely will not be buying $4 cups of coffee or even $5 to $8 fast food meals, often the price of "free" WiFi.
There are places where merchants collectively support a free downtown WiFi, but I am finding more often now that it is the municipality and they connect you to their site to collect a daily fee ($3-5) before letting you get to the Internet.
Libraries often have a free connection. Some, it is for anybody. Others, for card holders, and they will often let non-residents buy a guest card good for some period from a day to a month. That is usually all about being able to identify someone when terms of service are abused.
