It varies a lot based on what you want you for additional tubes beyond what the rule book requires as a minimum.  I also varies a lot based on what you expect the cage builder to do in preparation of installing the cage.  Is he going to strip the interior?  Is the dash and wiring still in place? 

You can figure on about $1800 on the very low end assuming you find the right (cheap) builder.  I would say a more expected norm would be $2200 - $3500.   

Dave

Great! Thanks for the info.