You definitely have your head in the right place. Getting a kit like the Hyper or Xray that you mentioned will give you alot better experience than going the RTR route. As mentioned above, get a quality steering servo (coreless, 150+ torque,.15 or fater reaction) , and a decent metal geared throttle servo (Z590 that came with your XS3 would be great). I would say go the starter box route, and get an engine with a sealed backplate (no rotostart, no pullstart) because it will perform better and be more reliable, since there are less moving parts to fail, and the sealed backplate is less prone to air leaks.

Figure 400 for car, 50 for receiver, 80 for steering servo, 50 for throttle, 110 for OS RG, 100 for heavy duty starter box. $790 plus shipping for a good setup, assuming you already have basic tools, nitro accessories (fuel bottles, plugs, etc), charger (hopefully peak detecting), paint, glue, silicone diff/shock oils, etc. from your previous cars.