In my experience I've found that the Sony subs are more likely to be copies so I would avoid that. I personally don't like the funky looking Kenwood 3010 sub either so I would recommend that you go for Pioneer instead. I think both the 311 and 3003 fall in your range. Original Pioneer boxes will have a small holographic sticker on them so look for that before buying.
As for the speakers I assume they're trying to sell you Kenwood 718s as that's the most popular item in the market. Keep in mind these speakers have been discontinued for a long time and it's really hard to find original ones now. The copy ones do work fine in most cases, it's just that for a longer term an original speaker would be much preferred. Try to find any speakers whose originality you can verify and go for it.
The amplifier seems to be a bit pricy but I'm not aware of the ongoing rates so I'll let someone else comment on that. My advice is don't go for high numbers on the amp, go for a better build quality.
Also I have not had to upgrade my battery or alternator yet even though I'm running 4 speakers on a 4 channel amp and 1 sub on a mono amp so I'd say no need to worry about that for now
