$1500 + attorney fees, etc ... so yeah, about $2K min ... more like $5K really.
Considering his site has been active for a long time, whereas the other domain has had basically nothing, and the name is somewhat unique, he might actually have a shot ...
The easiest option for him would be to negotiate (or have some do so on his behalf) purchase of the .com version ... even if it costs him several thousand, it's a worthwhile purchase in my view based on the traffic numbers he PMd me.
Ron