One thing to keep in mind with this greenphone product, is that it is not an end-consumer device. I've heard a lot of people complain about the high price, lack of this or lack of that (wifi, etc..). But keep in mind that this was a special limited run of units (I think they only ordered 1000 in the initial run). That automatically creates a higher per-unit cost. And, if you compare this against the normal cost of evaluation / development platforms, it really is about right in line. I've seen arm / xscale dev boards go for around $1500 or so.
Now, it would have been nice if Trolltech would have decided to make this a consumer device, with better power management (longer talk time / standby time), better radio, more expandability. But then they would be in compitition with their customers (the handset makers that they hope will start selling qtopia phone edition based phones). Also, the average person wouldn't buy it, because even with higher production runs it would still cost around $300 to $500 (that's about the going price for a Treo). The only way a consumer would get this is if it was offered subsidized by a carrier (i.e., so it appears as a "free" phone).
Personally, I think I'm going to go the do it yourself route. I'm not going to go as far as the Pocket Penguin group here is doing (buiding the circuit boards from scratch), howerver I was looking at getting a GumStix module, lcd, gsm module, and pack it all in either a regular phone housing (you can get the housings fairly cheap), or gut one of those $5 toy phones and use that for a housing. Total cost doing it this way would be around $450 or so, but it won't have that "finished" look and feel. Other option is to pick up a Motorola A780 and load up the userland replacement from open-ezx project. That may be the easier route, but then I'd be lacking a few hardware features.
