Why is there no bike like the Trek 1000 with just a bit more tire clearance in the $600 - $700 range?
Because the makers are convinced wannabe racers whose bikes are toys must be catered to. People who really use their bikes and value versatility are marginalized.
I would second the used idea.
The drawback is that it may take awhile to find the right bike, but you'll get so much more for your money. If you are mainly looking for a frame, you can find something more quickly.
I spent about $600 on my first commuter--a new bike--when I didn't know much about bikes. I just bought my second commuter for $350 (hardly used Bridgestone MB-1), and I'll probably put another $200 into it eventually to get it just how I want it. In the end, I'll spend $500-$600 for a bike that would cost me $1500 if I bought something comparable new.
If you don't like to work on your bike, or you need something right away, go new. If you want to get more for your money, find a quality used bike and customize as your heart desires and pocketbook allows. Personally I don't think I'll buy a new bike until I'm ready to get a custom frame. That's just my take.
On the new bike front I've only heard good things about the Bianchi Volpe. Because I get a shop discount I looked into getting one, but decided against it. Bianchi is having a hard time meeting demand with the Volpe. Not at all a bad price at $850, but still, if you have the patience, not a great deal when you consider what $850 would buy you used.
(Did anybody see the nearly mint Miyata 1000 that went for $500 on ebay a couple of days ago?)
--AK