Total costs are unknown. But if you really want the lowest total costs, buy a secondhand Isuzu Crosswind and drive it till it falls apart.
But seriously... Total costs will depend on how many kilometers you drive every year, unforseen/emergency repairs along the way, and how long you plan to keep the car. They should be similar, but note that the Focus, being merely a facelift, shares parts with previous Focus models.
For gas:
The Focus engine hasn't changed much. There's parts commonality between the 2.0 and the 1.8, and some aftermarket parts interchange between the Focus and the Mazda3 (though there are valvetrain, ECU-programming and internal transmission differences). Lots of sources for these parts, already... The 1.8 MT is particularly fun, though the interior sucks compared to the hatchback.
The Cruze is all-new, so the parts supply isn't there yet. But if it's popular enough, the traditional Chevy parts suppliers (like Thunder) should carry anything you'll need in the future. The gearshift doesn't feel quite as high-quality as in the Focus, though the rest of the interior is better. Steers well, but the Focus steers better.
Long-term costs will be similar to other 1.8 liter cars (barring any unforseen defects). With the Focus, you're getting a relatively trouble free car in its last generation. Most of the early issues (electrical, CV Joint) were ironed out with the pre-facelift. The only big difference is the stiffer suspension and some trim. Everything else is the same. Both cars have longer oil change intervals than their diesel counterparts, which keeps overall costs similar, barring any huge oil price jumps in the future.
The one thing that will suck is resale... people don't want big engined cars... I'm not quite sure if the 1.8s will count as "big engined" five years down the line when Honda Fits and Toyota Yarii have 1.8 liter engines and are as big as Starexes...

but you never know...
For the diesels:
Focus: The computer box and transmission are all-new, and the front-springs and geometry feel different, but for turbos, sensors, injectors, shocks, brakes and miscellaneous trim pieces, you should be able to use stuff from the previous generation Focus... and there are sources for many things and work-arounds for others. If you log in to the forums at Fordclubph.com, you can find resources for out-of-casa maintenance.
With the Cruze, you're getting an all-new diesel, albeit one shared with the Captiva, so there's some commonality there. Durability and maintenance are an unknown.
Neither car will be as simple to care for in the long-long run (150,000 kilometers plus) as their gasoline counterparts. Diesel quality here is still a joke, and these modern turbochargers are sensitive to poor maintenance and abuse. If you plan to keep them for about 80-100,000 kilometers, they're decent value, and at least the diesel engines will keep their resale value up against the negative "poor fuel economy" image (image: perception: in other words, what people think rather than the reality of the situation...) of American makes.