[dfink]

Depends on what you are wanting. A 3.6 is a nice power package you will get the desired grunt you are seeking. But not much to show off. Open the deck and Yep there it is.
Or you can do the WOW motor. The WOW motor will stand out in a crowd, rev like crazy and free up a lot of room for working on it. Now for cost. The cost for the motor itself was not that bad.
Heads rebuilt and twin plugged with race springs. $1300 - $1500 (forget the titanium keepers unless you just want to tell everyone you have titanium keepers.)
Pistons I would go 10.5:1 very drivable yet that little extra umph. $1100
Bore cylinders can't remember exactly I think around $1000
Cams reground to streetable grind $250
Arp rod bolts and steel head studs $500
Nose bearing $200
Chains, cam gears and ramps $300
Gasket set $300
Rods rebuilt - $300
Rockers rebuilt $250
Stuff I forgot - sealants etc $500
Pretty stuff like powder coating $500
So basic engine say $6500 if you do all the work

Now the fun stuff
PMO throttle bodies with Electromotive TEC3r $8000
PLX-O2 sensor $250
Plug wires top and bottom $500
Headers $1200
New clutch $1200

Somewhere around $18000 if you do all the work will get you a very cool, very streetable, 275 RWHP flat 6. Probably another $500 - 600 to tune it. I would guess that is a $25,000 build if you pay to have it all done.

I don't know what to do for one in between. My stock 3.2 pulled 203 RWHP on a dynojet. You could just redo the cams in the 3.2 put on the headers get a chip and have a decent running car. Put the money saved in the suspension you will probably go faster that way.