HDR Processing could be done using open source tools. Here are the tools that could get you started. 

QTPFSGUI

used to create a HDR 

  1. Create a HDR image from the input images. 
  2. Tonemap the created HDR image. 

ENFUSE

It is a process similar to HDR, except that the images are fused with one another. It has its own advantages and disadvantages. 

GIMP

used to finish off the HDR

  1. Masking . Usually the LDR created from the created from QTPFSGUI, need to be placed on top of the original image, mask out some portions. 
  2. Curves, Levels, Saturation.
  3. Adjusting RGB channels.

Download Links

  1. QTPFSGUI - http://qtpfsgui.sourceforge.net/?page_id=10
  2. Enfuse - http://wiki.panotools.org/Enfuse
  3. GIMP - http://www.gimp.org/downloads/