You can't? It's impossible? I can think of three ways, off the dome, you could do this without AI.

1- stock photo images and vocaloid voices, using an audio overlay so it sounds like it's just a weird interference.

2- literally use friends, family, and their friends and family for the project. Random people from the Internet who would have fun with it. Anyone who needs to pad their portfolio for acting, headshots, and voicework. Network your solution.

3- do a patrion or go fund me or whatever and one of the tiers, or the lowest tier, is that you get to be in the game.

Hell, for bonus ideas that are things you thought of already, just draw em and do so the voices and it'll be crappy but that's fun, actually bite the bullet and pay people, or like you said, do without.

Using AI is giving up. All those games where part of the appeal was the effort they put into it would be nothingburgers if they used AI. Cuphead took off because it was all hand animated, and if they used regular computer animation people wouldn't have cared half as much, and now it's got it's own cartoon and people are still buying merch for it.

So yeah, if you wanna cut corners and use AI, go right ahead, but people will know you decided to waste a huge amount of energy and water to make a lower end product.

Or... you could always figure something else out and let people see the effort you put into this project you care about, and let that effort be part of the selling point. We want games people put effort into, so please don't water down your grand idea with slop.