I don't know too much about 6.0's but having owned a 6.4 in the past I'll say this. IDP or GH tunes on a 6.4 will easily exceed 600 hp on all factory items, including the air filter. And is DD for most people.
In the end, "budget" and "hp" usually don't mesh well in the same sentence.
Not trying to sound like a d$ck but for 600 hp here is some info
http://powerstrokearmy.com/forums/showthread.php?t=1044
and non-vgt
http://powerstrokearmy.com/forums/showthread.php?t=19940
Do some searching as what you are asking, a lot of info is already out there. There are unique situations but IMHO, asking how to make 600 hp is pretty standard fare.
Make an itemized list of what you have so that may help someone who may have been exactly where you are but expect to buy Injectors (190-205's)
http://swampsdiesel.com/prestashop/en/injectors/57-190cc-100.html , Trans(stage 3)
http://www.twisteddieselperformance.com/twisted-diesel-transmission-level-3-5r/ and the RR +/- 600 bucks and possible accompanying fuel system and the t4 set up, pipes and turbo. Those items alone should be in the 15-18k range.
Several vendors have what you're looking for. I saw that cutting-edge diesel has some items, so does Swamps and MPD. Maybe just call them tell them you want 600 hp so you get some info on any hidden cost.
Good luck!