I regularly make quiche using 3 eggs and 1 cup fat free half and half. I put the filling in the crust shell (ham and veg for instance), add cheese, about a cup or so, and pour the beaten eggs combined with tthe half and half over all this. I typically add any spices or herbs to the egg/half and half mix before pouring over the other stuff.

cream doesn't have the same lactic issues(it is fat with little lactose and in fact slows down the absorption of lactose making milk easier to digest) as milk so that shouldn't be a problem. But really you can substitute milk for the cream it just won't be as rich or have the same mouthfeel. There are all kinds of custard fillings that do not use cream. Try 4 large eggs, 2 1/2 cup of milk for the custard. Blind bake the crust and whatever filling you are using make sure it isn't going to exude lots of liquid or precook it and make sure it isn't super juicy and then whatever cheese, about a cup , you want blend half into the custard and put the other half on top.

I've had success substituting fat free yogurt. It gives the custard a nice tang and is very complimentary depending on your fillings. It's great with Swiss cheese, bacon and scallions.

You could also try soy milk. Soy behaves well in pies, sweet or savory. It tastes great in a vegetable-laden quiche.

As amysarah said, you need the cream to make the custard, so if your need to substitute the cream is caloric and not lactic in nature, you can try fat free half and half. It has a thicker constistancy to emulsify the egg mixture.

A quiche filling is essentially a custard; so as with any custard, you can substitute milk for part or all of the cream in a recipe. (Of course, with milk it won't be as rich and creamy.)

If you're going to sub, I'd at least use whole milk - low/non-fat would give too anemic a texture, I'd think.