The correct answer is: I made made my own barrel but you can buy them pretty cheaply now.
The main idea: Rain barrels are easy to install and use.
This idea needs to be supported with a sentence that relates in a logical and coherent way with it's content. In other words the following sentences need to demonstrate the reasons they barrel are cheap and easy to install, examples and facts can be given.
In the sentence chosen the author says that he made his own barrel, in this way he tries to show us that anyone can do it, an expert is not needed to perform this task, therefore they are "easy to install and use". By mentioning the low price he makes an implied relation, we associate cheap things with simple things, if the barrel was a complicated thing to use they would probably be more expensive.
The other options given just give general information related to barrels but are not able to connect with the main idea.
