Figure it like this:
Servos - $150-250 (Savox are alot less expensive but there are some REALLY expensive servos out there)
Engine/Pipe - $275-600 (Werks B6/2058 would be my suggestion and cost ~$275 if you go through Tower...)
Starter Box - $100 (Trust me on this one get the Ofna Blue Truggy starter box)
Radio - $50-500 (If you are racing get a KO EX-10 or Airtronics M11x)
Batteries - ~$100 including a good receiver pack and LiPo for your starter box
Charger - $50-199 (A quality charger will last you a lifetime dont go cheap...)
Fuel Bottle/Tools/Misc - $25-200
Sooo ~$750+
OR you could get an 8IGHT RTR for $600 and it comes with everything above including a great starter radio except batteries, a fuel bottle and Glow Igniter... You can also use it as a platform to grow on...
***Edit***
In my experience a typical buggy/truggy build is ~$1200 in all if you already have a starter box and radio