Sounds a little high but could depend on the model and options.
There is a Yahoo forum on Aframe trailers at:
http://autos.groups.yahoo.com/group/alinerchaleta-frames/
Lots of helpful folks with Chalet and Aliner experience.

NADA doesn't list a Chalet before 2001.  Is it maybe a Chateau?  A '96
Chateau only lists for $2000.  But you would need the model name and the
length to get an accurate price.  But $4000 for a 10 year old is a
little pricey.

And I bet he is really hoping that you will give him that much money for it.
I would not pay that much.  I realize that this is apples and oranges, but
my 2 data points are that my smashed 1994 Coleman Destiny Rio Grande
calculated out to about $2300 when the insurance company totaled it and the
replacement excellent condition Coachmen Clipper 1998 cost me $2500 to buy
used a couple of months ago.  Both are soft sided mid-level popups, thus the
disparity in fruit, but to me the Chalet is way smaller and less useful for
me.

Call your insurance company and see what they would value it at, going on a
pretense that you might add it to your policy.  Get the VIN number - they
seem to be able to do magic with that.

Let us know what you do and why so we can all learn from the experience,
thanks.
Tomes

We had 1994 Chalet in excellent condition- gave 3500.00 in 2002.  We loved
the trailer, biggest drawback was no shower or toilet. Also of concern, if
you are going to be using the trailer in really hot climates - Texas  -
something about the shape of the trailer impedes airflow from a front
mounted A/C. Never could get ours cool and keep it cool in the summer
months. I understand there is still an issue with that, even in the newer
models.