Piety is like a religious faith. This is saying he mostly only cared about his religion and the only thing he cared about more than religion was saving money and being stingy. 

Hope that helps :) 

Thank you for your question.

I admire the fact that you want to understand

fully what is being said, but it's a bit complicated and may

not be worth your time.

In general-

The author is giving the readers in English an idea of

what the ancestors of "scout" were like in the book.

This is a very familiar idea of White-Anglo-Saxon-Protestants

that settled parts of what is now United States territory.

The Calvinistic ideas and mode of living of the the first Finch ancestors

would be very well understood and familiar to people living in the United States

today. 

So, it would be a little hard to explain to you, just as it would be

perhaps hard for you to explain to me how persons living in 14th

century Korea were like in a Western context.

Suffice it to say.  Simon Finch was probably a very industrious man, but

also not very pleasant.  He was very religious and worked very many long hours

and was not extravagant in the way he spent his money.

He probably was harsh at times with his family too, as in the Calvinist-style.

Basically, this sentence is telling you that his sense of stinginess is greater than his piety. So, although he might have been quite religious, his stinginess is a bigger trait in his character.

This is my understanding of that sentence. I hope that answers your question :)