If you don't mind some conversion steps the EB1150 by Ebookwise is VERY sturdy. Bad news? It uses the imp format which means you need to convert most books to make them work on it. Good news? One of the cheapest ereaders out there, don't let the price fool you though it really is a great machine!
Other than the EB1150 I don't get the feeling that many of the ereaders are very sturdy? The e-ink readers are very light weight and spendy. Maybe a iphone or non-phone iphone? You can get insurance for them so if he breaks it you can get a replacement.