Setup right field type and widget for field
For the first issue you can actually add it as a key|label pair. 

Where the key would be the number and the Label would be what is displayed. for example 5|buy 1 at 5 

this would show "buy 1 at 5" in the dropdown but the value would be five. you want to work with numbers you might want to select List(integer) as your field type. 

For the second problem you might want to take a look at the Cloud Zoom Module.


  This addon provides a small, thumbnail sized image, with an on-hover
  popup, zoomed and centred on a larger version of the image.


OR 

jQZoom


  The jQZoom module is a wrapper for the jQuery plugin jQZoom. The
  module provides a javascript magnification effect for images. When a
  user mouses over an image, a larger version of the area under the
  cursor will be displayed beside the image.