VG30DE motors i assume thats what kind you have right now , well for a motor with about 45-55 k on it it should go for about 1K - 1500 for the motor itself!
But then again the motor your looking at has double the mileage but it comes with the ecu tranny and misc stuff (basically the whole front clip) i say for price range 800 - 1000 would be a good price since the motor has such a high mileage.
if i where you i believe old school american V8 will fit nicely in there. ive seen a few with a small block and also a big block but the big blocks needed a little extra work to get it to fit. Not to mention the weight of the car with all that torque it can turn into a pretty fast car
im currently working on a 72 datsun 510 blue bird and ive kinda scratched the SR20DETT and going with a big block V8 454 cubic inch
(still measureing and testing right now though)