New "Computer" Needed

My car would start, drive some 35 miles, and after a wait of an hour, wouldn’t start again. The battery was replaced and the next day, same problem. The alternator and starter test fine and I am told that the problem is in the “computer” - the security system is telling the auto lockup to occur. The red security light on the dashboard does come on after driving a short distance. I am told the “computer” will cost about $1100. Does this sound like the probable cause and a reasonable cost to repair?

No, Not The Probable Cause.
What Make, Model, Model-Year, Is This Vehicle ?
How Many Miles On It ?
Who Told You That You Need A Computer ?

CSA

Year, make, model?

It could be reasonable. Just agree ahead of time what the shop will do if the replacement part doesn’t fix the problem.

If it does turn out to be a faulty ECM, then you might want to consider a rebuilt rather than new. Rebuilt will cost less and is likely to be better than new as most of the electronic components will be burned in to a greater extent than new components.

I had a 1980s ECM failure. New as I recall was around $700; rebuilt was around $300 or $400.

Chrysler Sebring 2000 90K mi Repair shop who installed new battery said computer must be replaced.

2000 Chrysler Sebring

Since very similar problems occour with the GM Passlock II system an entire industry revolves around by-passing Passlock II. Have you “googled” "How can I by-pass the (good time to find out the exact name of your system)on my 2000 Sebring? Perhaps the same type equipment exists for your Sebring.