whoa..that was kinda confusing..
something about motors to where your shifter is to body mods....
anyway, as far as building a brand new 3.3 or 3.5, unless you've got castings for the block/heads/etc, a brand-new motor isn't gonna happen. The closest you could probably come would be to to get an engine from ATK-Engines.com and do head work/cylinder honing, etc yourself. Then you gotta get different parts to accept anymore horsepower you throw at it, etc. As for a cost, well, figuring that ATK sells motors at about $3g's plus core...well there ya go.
As for different engines, if you rerouted your exaust, measured up the transmission hump, and made different motor mounts and a fair amount of engine bay fabrication, you could maybe stuff a Mopar small block into the car. Then you gotta get all the stuff for a rearwheel drive car (rear-end, gears, axles, driveshaft, etc).
But that's only if you want V8 power. If you want some other rinky-dink 4 or 6-banger that's FWD, i'd say buy the car that already has it.