I've spent hours searching for a 12v 30A latching, bistable relay that can be triggered with a 5v signal (from an Arduino, of course) and that does not draw any current one the latching state is set. There are lots of latching relay that can be triggered with a 12v signal. There are lots of latching relays that can be triggered with 5v but can only handle 10A or 15A. There are also lots of relays that come close but that require current to maintain the 'latch'.
I also need to design this for manufacturing so I need an inexpensive option, e.g., under $10 retail, which I should be able to acquire for about $2 - $3 in bulk.
Looks like you are asking for the moon on a stick.
If you find something that can be triggered from 5V, then the current it will take to make it latch will be very high.
It is like squeezing a balloon, as you squeeze one part of your specification, another section expands. You seem to want it all, and for a silly price. Mechanical relays are expensive, first of all because of the latching mechanism and next because to generate a large magnetic field you need lots of copper wire, or a high voltage.
Hobby electronics sits on the back of commercial electronics, like a flea on the back of a giant. The industry will only supply what there is a demand for.
You would need a mosfet driver and drive the coil from 12V. Or actually 2 mosfets as you want a latching relay.
But as said: 2 Euro is not realistic...
Take a look at car main beam light relays. Those are latching and 12V and 30A...
The combination of "I can't find thing" and "I need to manufacture in bulk" is something to be wary of. IME, if it's something that's hard to find, there's usually a good reason for that, and it will come back to bite me if I rely on being able to find large amounts of it in the future.
Your spec doesn't look easy to meet.
I'd consider designing a small voltage boost circuit (potentially using the relay coil itself!) to get from 5V to 12V and using a latching relay with 12V coil.
Thank you, all. Great feedback. I honestly just thought I must be looking in the wrong places. So yeah, @Grumpy_Mike , I suppose I truly was asking for the moon on a stick. I have considered the 'boost circuit' approach, i.e. driving the relay trigger with 12v instead of 5v, e.g., utilizing a mosfet for trigger logistics... indeed using the coil current itself, as you say, @cedarlakeinstruments. As you say, @build_1971, for this approach there are ample inexpensive automotive relays. None of this is complicated, but if a good-fit relay existed then it just felt like superfluous componentry.
@dougp Great diagram... love that you just whipped that out.
BTW, @Paul_KD7HB , thanks for pointing out the reliability question. Luckily, the duty cycle is low and switching speed is not a concern.
I think 
