I hadn't planned on making another submission, but after tinkering with it a bit I realized 
a few things:

1. A simple GUI would be nice.  I used FXRuby.
2. The SAX Listener was barfing when the number of vendors was six or more.  Funny thing was
 that it only had a problem when the XML was formatted.  If I removed the whitespace it did 
just fine.  In any case, I switched to using a StreamListener instead.
3. There was an inconsistency in the logic in my original in_range? method.

Anyway, here is the Ruby code followed by sample XML:
--------------------------------------------------------------
#!/usr/local/bin/ruby -w
require 'rexml/document'
require 'rexml/streamlistener'
require 'fox16'
include Fox

class VendorListener 
  include REXML::StreamListener
  def initialize(low_price, high_price, vendor_search_window)
    begin
      @low_price = Float(low_price)
    rescue
      @low_price = 0
    end
    
    begin
      @high_price = Float(high_price)
    rescue
      #if someone can spend more than this then
      #she or he can afford a better program
      @high_price = 10**15
    end
    
    @vdr_srch_wdw = vendor_search_window
  end
  
  def tag_start(name, attrs)
    if name == 'Vendor'
      @vendor_name = attrs['name']
    end
  end
  
  def tag_end(name)
    if name == 'Vendor' and 
      if in_range?
        @vdr_srch_wdw.add_vendor(@vendor_name)
      end
    elsif name == 'LowPrice'
      @vendor_low_price = Float(@data)
    elsif name == 'HighPrice'
      @vendor_high_price = Float(@data)
    end
  end

  def text(text)
    @data = text
  end

  def in_range?
    @low_price <= @high_price and
      (@low_price > = @vendor_low_price or @high_price >= @vendor_low_price) and
      (@low_price <= @vendor_high_price or @high_price <= @vendor_high_price)
  end
end

class VendorSearchWindow < FXMainWindow
  def initialize(app)
    # Invoke base class initialize first
    super(app, "Ruby Quiz \#164: Vendor Search", nil, nil, DECOR_TITLE | DECOR_CLOSE)

    #Add text field frame at the top
    textfields = FXHorizontalFrame.new(self, LAYOUT_SIDE_TOP|LAYOUT_CENTER_X)
    FXLabel.new(textfields, "Enter a range:", nil, JUSTIFY_LEFT)
    FXLabel.new(textfields, "low:", nil, JUSTIFY_RIGHT)
    @low_field = FXTextField.new(textfields, 10, nil, 0, JUSTIFY_RIGHT|FRAME_SUNKEN|FRAME_TH
ICK|LAYOUT_SIDE_TOP)
    FXLabel.new(textfields, "high:", nil, JUSTIFY_RIGHT)
    @high_field = FXTextField.new(textfields, 10, nil, 0, JUSTIFY_RIGHT|FRAME_SUNKEN|FRAME_T
HICK|LAYOUT_SIDE_TOP)
    
    #add button frame at the bottom
    buttons = FXHorizontalFrame.new(self, LAYOUT_SIDE_BOTTOM|LAYOUT_CENTER_X|PACK_UNIFORM_WI
DTH)
    show_button = FXButton.new(buttons, "Show Vendors")
    show_button.connect(SEL_COMMAND, method(:on_show_vendors))
    exit_button = FXButton.new(buttons, "Exit")
    exit_button.connect(SEL_COMMAND, method(:on_exit))

    #Place the list in a sunken frame
    sunken_frame = FXHorizontalFrame.new(self,
            LAYOUT_FILL_X|LAYOUT_FILL_Y|FRAME_SUNKEN|FRAME_THICK, :padding =>  0)
    @vendor_list = FXList.new(sunken_frame, :opts =>  LIST_SINGLESELECT|LAYOUT_FILL_X|LAYOUT_
FILL_Y)
  end

  def on_exit(sender, sel, ptr)
    getApp().exit
  end
  
  def on_show_vendors(sender, sel, ptr)
    @vendor_list.clearItems(false)
    REXML::Document.parse_stream(File.new('vendors.xml' ),
      VendorListener.new(@low_field.text, @high_field.text, self))
  end
  
  def add_vendor(vndr_name)
    @vendor_list.appendItem(vndr_name)
  end
  
  def create
    super
    show(PLACEMENT_SCREEN)
  end
end

application = FXApp.new
VendorSearchWindow.new(application)
application.create
application.run
--------------------------------------------------------------
<?xml version="1.0" encoding="UTF-8"?> 
<Vendors> 
    <Vendor name="Company A"> 
        <PriceRange> 
            <LowPrice> 1000</LowPrice>
            <HighPrice> 3000</HighPrice>
        </PriceRange> 
    </Vendor> 
    <Vendor name="Company B"> 
        <PriceRange> 
            <LowPrice> 6000</LowPrice>
            <HighPrice> 10000</HighPrice>
        </PriceRange> 
    </Vendor> 
    <Vendor name="Company C"> 
        <PriceRange> 
            <LowPrice> 500</LowPrice>
            <HighPrice> 2500</HighPrice>
        </PriceRange> 
    </Vendor> 
</Vendors> 



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