"The BBC’s solitary HD channel is broadcast free of charge over Freesat, "
It's certainly broadcast free of charge, but "all" Freesat adds is the EPG (electronic programme Guide). This is not a Freesat box.
"And since Humax's promised Freesat HD capable DVR is set to retail for around £299,"
It's already been launched for £293 (with 15% VAT), although in very short supply at present.