Copy specific text from email message to spreadsheet - email

Question

I get my checking account balance emailed to me once per day. I want to use Google Apps Script to pull the balance from the email message and plug it into my checking account spreadsheet. I am a novice to coding, but so far I have figured out how to do the following, which gets me a log of HTML code of the correct email message:
function myFunction() {
var thread = GmailApp.getUserLabelByName("CHK BAL").getThreads(0,1)[0]; // get first thread in inbox
var message = thread.getMessages()[0]; // get first message
Logger.log(message.getBody()); // log contents of the body
}
However, because this method returns the HTML code for the email message and not the actual message text, it doesn't contain the balance number that shows up in the email itself.
I tried substituting getPlainBody in place of getBody, but it returns a null value in the Log.
The question posted here is pretty much my same question (Google script that find text in my gmail and adds it to a spreadsheet?), but even with Mogsdad's reply and helpful links I haven't been able to figure out what's going wrong.
Can anyone help redirect me on how to get the email content instead of the null value?
(Once that's solved, I can't say that the link on Mogsdad's other reply is very clear about how to identify the currency and copy it into the spreadsheet, but of course I haven't been able to play around yet since I can't even access the content yet.)
Thanks!
EDIT 1
See Serge's answer below for instructions on how to parse the HTML. I used those functions to grab the text of the most recent Bank Account Balance email from a Gmail label/filter and drop it into a cell in my spreadsheet.
Then I was able to use the following equation in an adjacent cell to strip it down to just the currency number:
LEFT(RIGHT(A5,LEN(A5)-FIND("$",A5)),FIND(CHAR(10),RIGHT(A5,LEN(A5)-FIND("$",A5)))-1)+0
Of course, this works for me because the currency number is always preceded by $ (the first, and in my case, only $ to appear in the text) and always followed by CHAR(10). Anyone trying to apply this formula would need similar consistency before and after the value they are seeking to isolate.

Answer 1

You could try this code snippet originally written by Corey G on SO to get the text from the html content. I use it quite often and it works nicely most of the time :) (Thanks Corey)
function getTextFromHtml(html) {
return getTextFromNode(Xml.parse(html, true).getElement());
}
function getTextFromNode(x) {
switch(x.toString()) {
case 'XmlText': return x.toXmlString();
case 'XmlElement': return x.getNodes().map(getTextFromNode).join('');
default: return '';
}
}
And a test function to try it :
function test(){
var html = GmailApp.getInboxThreads()[0].getMessages()[0].getBody();
throw(getTextFromHtml(html));
}

Answer 2

As to why getPlainBody() is returning null, it is most likely due to a bug in Google Apps Script. The issue has been filed at https://code.google.com/p/google-apps-script-issues/issues/detail?id=3980.
From that thread: "It seems the messages affected contain HTML in their content. A possible workaround involves using getBody() instead of getPlainBody() and parsing through the HTML directly."