New Product w/ 42 Vine Reviews (4.9 Stars) – Bidding is Out of Control at $40 Price Point. How do I fix this?

Heads up, if you're heavy on Vine reviews right now. With Amazon getting stricter, there's a chance some of those could still get whacked even if they're legit. Anyway, assuming your listing is solid—pics, copy, ratings all good—a 10%+ conversion rate at your price point isn't the end of the world. The real problem is your CPC is eating you alive and wrecking your ACOS.
Here's what I'd tweak right away: flip your auto campaign bidding from "down only" to "up and down." And seriously, cut that CPC in half from where it's at now. While you're at it, open up a separate broad match auto with a bid like 10% lower than your tight match. The main thing is, I'd probably start pulling back on the auto campaigns anyway. Don't rely on them for rankings. All they're really good for is checking if your listing is garbage or not. The real work should be in manual. Dig into your search term reports and pick out some solid AB/ABC root terms with actual search volume (use ABA data if you got it). Run them on broad or phrase match, negative out the junk roots from the start, and put your budget there to uncover some long-tail gems that actually convert.
And seriously, milk that 4.9 star rating for all it's worth. First off, get a Brand Store up and running if you haven't, and dump some budget into SBV. Second, go set up some ASIN targeting and go after every competitor with worse reviews, worse pricing, or a crappier offer than you. And while you're at it, open up a category placement ad too. You want all that related traffic you can get.

Your rating is fine, so we'll assume the listing itself is decent enough.

1. Double-check your auto campaign search terms or the ASINs it's attaching to. Is it actually relevant? If not, you might have some listing optimization to do.
2. You can't really lower a bid until a keyword is consistently converting. Right now, your auto campaign is spraying everywhere, so you can't get that stable performance on any specific word group to lower bids.
3. You gotta pick a lane for your keywords. Test broad/phrase/exact to see what CPC actually gets you in the game for each type. Pick one match type that works, stick with it, and build up the weight on those keywords. Watch your search terms like a hawk to figure out which keywords deserve the high-exact-match treatment. And for the love of everything, go HAM on budget during deals or Prime events. That's when you really build weight.

Bottom line: Pick your keyword direction, build weight on them, then use events to hammer your best converting exact terms.

I'd scope out your top 3-5 competitors that have similar review counts and actually look decent. See what keywords are driving their traffic and then build a manual campaign around those.

First rule of fight club is negative keywords. Get rid of the junk, stop lighting money on fire. Also, take a hard look at your price versus your competitors. Throwing money at ads without fixing the actual product page is just treating the symptom, not the disease.

1. CTR is kinda low, but your CVR is okay. Looking at your screenshot, I'd probably focus on the "rest of search" placement. Tight match with fixed bids is fine. Maybe try a separate broad match campaign on a shoestring budget just to test the waters. 2. Get ahead of the game and build a negative keyword list now, stop wasting money. 3. Pick 2 or 3 second or third-tier keywords. Set them up in their own ad groups with phrase match, fixed bids, and put a healthy multiplier on "rest of search" placements to see what happens. That'd be my first move.