'98 Jetta Dead Battery, Dead Computer ... what else?

We have 98 Jetta with over 100K miles, great shape, regular oil changes, etc. One morning, the engine doesn’t start. We tow it to mechanic who says the battery is dead and then later says the computer died. He says total repair estimate is $1500-$4000 and once computer is replaced, may find other problems. What gives?

Get a second opinion.
Computer deaths are almost unheard of on these cars.