I use the karlie heavy duty clippers on large dogs, they're only around 6 quid a pair I get at new pair when they start going blunt, they're more like scissors than guillotine types, I've also got a pair of the mars superior clippers but they're about £30, very strong, but IMO it's down to sharpness so I use the karlie ones and just treat the as disposable after a couple of months, mind I'm a dog groomer so they'd probably last you a bit longer
You could also cut the nails once and, if your made of money, buy a nail grinder, not sure if your dog would put up with it though
Cutting nails is easy with practice, quicker the better, just get some trimmex styptic powder if you cut the quick then use a bit if that to stop the bleeding, oh and here's a tip, trim the nails and hair in the pads of the feet before you bath the dog, that way the feet dry quicker and if you do accidentally cut the quick, then the foot won't be bloodstained after, oh the longer you leave the nail to grow, the longer the quick will be, so long nails means your more likely to nick it when you take the nails shorter
I get most of my stuff from here.
http://www.groomers-online.com/section.php/50/1/nail-care