The caprice will be much more expensive, I would think. I picked up a running LS400 with no papers for $500. When I couldn't get rid of it after snaking the engine/trans, I had to chop it into pieces for the scrap yard. What I found in doing so left me pretty surprised. The pillars were filled with this squishy, dense foam, and there was a ton of sound deadening. The body harness had these molded plastic clamshell cases running the entirety of it. I don't have much to compare it to besides economy cars from the 70s, but it had me thinking, "Wow, this is a quality machine," the whole time I was chopping it up. Also, the 1UZ is a pretty great engine, albeit pretty slow in that heavy car. It's a shame Yamaha never designed cylinder heads for it. If I wanted to hotrod it, I would find a caprice. If I wanted a cheap luxury sedan, I would get the LS400. Expect the front suspension to need to be rebuilt on the LS400, and the interiors are probably going to be thrashed in most of them.
1UZ
>million mile engine
>6 bolt mains
>all aluminum
>quad overhead cam 32 valve
>a manual swap will cost $$$
>slow
>barely any aftermarket
>pre vvti will have thicker rods for boost
>vvti engines will have almost 300hp

Caprice engine
>probably has a 305 unfortunately
>HUGE aftermarket
>parts are cheap and available
>can build an inexpensive 350 vortex to swap in that will make 400hp just by breathing on it