If you do not have alot of hills/climbing you can get a cheaper steel heavy bike. Parts on the other hand should be better quality as you will be using and overhauling the bike alot. Stainless steel chain, brooks saddles ect are not unreasonable if you use the bike alot. Tires and anything that prevents flats should be top notch.
You might start with a cheap used bike and see what it's flaws are. Then buy new or upgrade as you see fit.
2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.