What was the last Yakuza game you've actually played? I'm fairly certain English voiceover work was never attempted past the first game. I also don't see how performing the translation during development would decrease costs; if anything, that's just creating a bottleneck during master production and potentially delaying the game as a whole, which is in itself a cost.
The last one I played was 2. And I'm not saying it would decrease costs, i'm saying it would be a cost that, when compared to the rest of the project, is negligible and allows the game to be sold digitally in other regions with the least risk possible. Yakuza 4 was still a game who's distribution model was still predominately retail, the digital version taking far longer to come out than the pressed disc version, and I'm sure that the cost of releasing that game on disc in north america far outweighed the cost to build in english translation. With this stuff that's considered niche, now more than ever, developers and publishers have to depend on a digital only strategy to eek out the maximum amount of money on each project. Not releasing your games in other regions because it doesn't do well with the general video game playing market doesn't make sense when your audience would be more than happy to simply download your game via PSN or XBLA or Steam. Sega, or rather Sega of Japan, doesn't understand this yet, which is why so many projects end up just on the cutting room floor after a quiet Japanese release. It's old thinking that isn't going to be able to stand in this new generation, especially now that its (supposedly) easier than ever to put these games on these digital marketplaces for, in a lot of cases, next to nothing.
So like I said, forgo the american celebrity voice acting fanfare, spend money only on translation that makes the game understandable in story and gameplay, release the game digitally only outside of japan, and reap as much benefit from the rest of the world as you can without spending your budget on physical elements. It's a worldwide market now, hiding in your region isn't going make your company grow.