Raising chicks outside? Without heat lamp?

Ok so I'm probably going to be getting some baby chicks pretty soon. From what I am told they are about 2 weeks old.
I am wondering if I can raise them outside (in a secure shelter) without a heat lamp. It's been consistently in the 80's and 90's during the day and drops down to about the low 70's at night. Would the chicks be too cold or too hot? Also, when would be a good age to start letting them out to forage? My goal is to allow them to forage more most of, if not all of their food when they're old enough to free range.

Foraging is definitely a good way to lower the feed bill. Quality of forage and amount of area plays a large roll in how much it offsets. Can a chicken grow and live off the land? Yes. It wont reach it's potential of growth or egg laying without source of balanced feed though. Also in a free range situation, especially so if limiting feed, they will range farther and farther out attempting to get that nutrition. Neighbors and such need to be considered- your animals must be contained to your land. Free range flocks are at high risk. Many do it but know many also loose a lot of birds, others loose few and accept the risk involved.

Two weeks is a bit young to want no heat. If they were closer to three weeks of age then no problem. 70 F at night is great. At 3.5 weeks mine go outside if lows in 40's. But there is a huge difference in feathering in that week of growth. Your so close. Few more birds for self heating or few more days of feather growth and no problem. Is there anyway they'll hold them until 2.5 to 3 weeks of age?

Egghead brought up a lot of great points, but I'd like to stress the fact that your chicks will be extremely vulnerable to predators until they're around four months old.

Would you mind sharing in which geographical area you live so we might have a better idea of what kind of conditions your chicks will be facing?