Non-isolated DC power distribution for an appliance
Cheapest:
Possibly Option 1-- 24V/300W power supplies are widely available from many suppliers.  Actually, you'll need 450W out of the lower power supply, so that may put you above the cost of Option 4: a 48V/300W power supply and a 24V/300W power supply.  Again, both are common voltage and power ratings, and you can probably even find them in the same form factor.

Most Compact/simplest to wire:
Option 2, if you can find a suitable supply.  24V+48V/600W is not as common of a configuration, but there are manufacturers that will do semi-custom configurations using a modular design if you're willing to order in sufficient quantity.

100-250VAC input supplies are extremely common, I would venture to say that most of the enclosed or open-frame power supplies on the market will meet your needs there.

Regarding EMI, this is not likely to be a significant defining factor between your options.  It comes down mostly to the quality of the supplies you select, the nature of your load, overall wiring, etc.  You pretty much have the same options for adding any additional filtering you find to be necessary in any of your proposed configurations.

As far as efficiency, this largely depends on the nature of your load and where it fits in the efficiency graph of your PSU.  Going for a single larger supply may give you more PFC-equipped power supplies to choose from, if that matters to you.

So on the whole, your best bet is to start looking at what power supplies are available and seeing what best fits your cost target and your mechanical envelope.