I want to buy my son a cot for boyscout campouts.Something light weight and not to expenseive.

Skip the cot and get him a good sleeping pad like a Thermarest.  I have used these for years and they are much better than cots or conventional air mattresses.  They keep you warmer in cold climates by getting you off the ground, but not being such a large air mass that you body can't heat it up.  (like large, cheap air mattresses)  In all honesty though I went through years of the Boy Scouts with nothing but a sleeping bag.  Unless I'm camping in cold weather, I leave the Thermarest home.

I will check it out .And this winter they are doing snow camp so i was trying to get him off the ground .I did buy him a sub zero rated sleeping bag last year but i didnt spend much so i was looking for options .Thanks .

Cots are really to heavy and bulky to be practical.  

As the other post mentioned, get him a good self inflating sleeping pad.

getting him off the ground will make him colder! Due to the airflow all the way around him.

Get him one of the tarps that siver on 1 side to put down then hit mat then his bag.  Also make sue he knows to change down to SKIN and put on fresh clean dry clothing before going to sleep. The moisture content in his days clothes will make him shiver all night.

good points thanks