Very little (I assume you're talking domestic here)
Biggest difference is the availability (ie red-e-deals sell out quicker), also Points Upgrades aren't available on red-e-deals. Cost to change is the same.
Another thing to note is that if you think you're going to change dates a couple of times or more you might want to think about a Flexi-Saver or Fully Flexible ticket.
More details are here:
http://www.qantas.com.au/regions/dyn...UAURED_SUMMARY
and here:
http://www.qantas.com.au/agents/dyn/...eCardAug07.pdf