Looking at for some other stuff, sliver solder
does not seem to be that high priced compared
to the lead stuff.
The problem is not the cost, nor the fact you need a slightly hotter
iron. There are worries that it's not reliable (there are exceptions in
the RoHS directives for military and medical electronics, IIRC. Draw your
own conclusions...). Certainly there are a _lot_ more dry joints (and I
don't mean joints that look dry, but genuine bad connections) in consumer
electronic devices using lead-free solder.
-tony