How to use webdriver to randomly click on a button with precondication - selenium

Question

I'm trying to write a test script with flight booking tickets scenario like this: Randomly click a button which description contains keyword "tax not included",then results shows; Randomly click a button which not contains keyword, then price shows.
For instance: Go to ebay.com and search "iPhone",in the search result page,randomly click a url which label contains keyword "Buy It Now"...
Anybody got a clean solution to that? Thanks in advance.
I have no clue to handle this case...
here is my code:
public void flightSchedule(){
if (be.isTextPresent(locator.getValue("tax_text"), 1000)){ //if keywords displays
ArrayList<WebElement> lists = (ArrayList<WebElement>) be.getBrowserCore().findElements(contains(text(),'tax not included'));
Random random = new Random();
int ra = random.nextInt(lists.size());
WebElement element = (WebElement) lists.get(ra);
}
the page source code is：
<div id="itemBarXI151" class="avt_column avt_column_trans">
<div class="b_avt_lst">
<div class="avt_trans">
<div class="avt_column_1st">
<div class="avt_column_sp">
<p>
<span class="highlight">new york city</span>
(tax not included)
</p>
</div>
<div class="avt_column_2nd">
</div>
<div class="c6">
<div class="c7"> </div>
<div class="c8">
<div class="a_booking">
<a id="openwrapperbtnXI147" class="btn_book" title="booking tickets" onfocus="this.blur();" hidefocus="on" href="##" data-evtdataid="XI147">
<span>
<b>booking</b>
</span>
</a>
</div>
</div>
my xpath is:"//div[#class='avt_column avt_column_trans'] [contains(text(),'booking')]",but it doesn't work.