For its intended market (heavy internet users) then I don't see why you would want to make it cheaper.
From what I read from your link, what you get with a BRCK, up & above a 3G Mobile phone is capability to switch over into multiple networks, this IMO, is too little a difference to justify spending the $200.
The way this could work is to make a BRCK with a lot more innovative features than an average Smartphone. From top of my head from someone who spends a few days in the bush, a few would be:
(1) Ability to sniff the littlest of 'network' that's available. Give me 10X capability over what I can get from my Smartphone...
(2) Make a BRCK a mobile GSM 'Tower' so that users with GSM Phones around the BRCK can actually use its GSM Network embedded OpenBTS
(3) Make a BRCK to have a simple embedded Server that can say hold mails, both incoming & outgoing in a seamless way and then sends and receives these out at certain intervals. Would be good if it can do the same for Social Networking say FB & Twitter (Every 10 mins it pulls your Twitts, and pushes new ones you have done)
Basically, it needs to be really innovative.