I did something weird just for the fun of it. I calculated what would happen if I spent $400 for a GT Traffic 3.0 then modified it to my taste. If I changed the wheels to Handspun Deore LX front and rear with a dynamo hub at the front, let's say with shipping and duty in Canada it might cost $360. And then let's say a crankset would cost $120 then SKS Chainboard chainguard, pedals, reflectors for pedals, grip tape for pedals (non-slip in rain), bottom bracket, aluminium cup for left side of bottom bracket, Falcon friction shifters $110, Busch & Muller dynamo light $120 and labor cost $90, I end up paying $1200. ($400 + $360 + $120 + $110 + $120 + $90 = $1200)

However, if I'm using the frame, fork, headset, headset spacers, stem, handlebars, grips, brake levers, brakes, seatpost clamp, seatpost and saddle on the GT Traffic 3.0, then buying piece by piece might only cost me $361.
Nashbar touring frame $100
Nashbar touring fork $50
headset $30
headset spacers $6
stem $25
handlebars $15
grips $5
brake levers $25
brakes $50
seatpost $15
seatpost clamp $5
saddle $35

So, in reality, buying the bike might be looked at as almost useless instead of building piece by piece EXCEPT if you're somewhat poor and can only replace parts one at a time. Well, OK, maybe some would need to be done at the same time like the crankset, bottom bracket, pedals and chainguard.

Whatever, it's interesting to look at it and think about it. I still think however that if you build a bike part by part and find excellent deals on some parts, it could be possible in theory to get a better bicycle for the money. I mean in Canada, the Trek 520 cost $1700 in a store. I think you may be able to do better than that with parts on sale. Plus, if you wanted flat bars instead of drop bars and a dynamo hub with dynamo light etc., it would be completely customized for you instead of being forced to accept what's available in a complete bike. I mean some complete bikes will include a Shimano BB-UN26 bottom bracket instead of the Shimano BB-UN54 and also a Shimano dynamo hub that has more than 6 watts of drag instead of their models that have only over 2 watts of drag. Plus, the dynamo light they'll put on there might only put out 25 lux of light instead of the models with either 40 lux of even 60 lux of light.

I suppose some people may want to accept a compromise except when you get to a point where you're fed up and think if you only live once, it may be worth it to have your dream bike at least once in your life even if someone eventually steals it.