It was not a valuable book, and so a poor man who could read very little bought it for a few coins.

（and为连词，so为副词)

语法结构分析：

分句(1)It was not a valuable book.

分句(2)and so a poor man who could read very little bought it for a few coins.

备注分句2带有一个由关系代词who引导定语从句who could read very little.(读书不是很多的）

（buy sth for +金钱；以...价格买下某物）

参考译文：但这不是一本贵重的书，一个文化程度并不高的穷人用几块黄铜的价格把书买了下来。

and so 看作为等于and therefore“，意思“因此，所以”其中，and为连词， so为副词

Madeira has an ideal climate, and so it is not surprising that it has become a tourist paradise.(and为连词，so为副词）

马德拉有一个理想气候，因此它为成为一个旅游天堂一点也不奇怪。

It was snowing, and so I could not go out.

天在下雪，所以我无法外出。

This ticket has passed its expiration date, and so it is now invalid.
这张票已过了有效期，所以现在作废了。

备注1：如果没有and,只有so, 那么就是并列连词引导表示因果关系的并列句。

It was not a valuable book, so a poor man who could read very little bought it for a few coins.

例如：There are no more chairs available, so you'll have to stand. 

没有椅子可以坐了，因此你不得不站。

备注2：如果没有so,只有and, 那么就是并列连词and引导也表示因果关系的并列句。

It was not a valuable book and  a poor man who could read very little bought it for a few coins.

例如：He worked hard and he passed the exam.

他学习很努力，因此，他就通过考试。

备注3：如果and 和so一起使用, 那么and为连词，副词so.引导也表示因果关系的并列句。

It was not a valuable book, and so a poor man who could read very little bought it for a few coins.

Madeira has an ideal climate, and so it is not surprising that it has become a tourist paradise.

马德拉有一个理想气候，因此它为成为一个旅游天堂一点也不奇怪。