Inline 6
It would be best to buy a turbo motor and swap it in along with the ecu. The turbo motor has lower compression, bigger injectors and oil squirters for the rods. The higher compression in the NA motor will limit you on boost. Turbo cars also got a much stronger tranny (R154), but the w58 will do fine til 350-400whp, then bye bye.
-Turbo motor, ecu and harness can me had for 1500ish. Make sure you retorque the head (Search for "Head Gasket")
-intercooler and piping
-aftermarket downpipe w/ high flow elbow
-good time to do an auto to manual swap if you are auto.
Then with the left over money
-high flow cat or test pipe
-3" min mandrel bent cat back
-K&N filtercharger or equivalent (not ebay)
-Boost gauge that'll read at least 15psi
-Manual or Electronic boost controller.
This will put you in that price range with some left. You'll only be able to boost to 11-12 psi before the ecu cuts fuel. There are ways around it, but you don't need that info just yet.