I built up my road bike, a formerly owned fixed gear, and my current commuter (which could also be used as a tourer) from ebay frames and parts. I am unsure if I actually saved money, but feel I gained overall factoring in the education benefits.
- Road frame was several years out of date and going for an unusually reasonable price. Commuter frame was a fair price. Got exactly what I expected in both cases.
- I overpaid for the 1st drivetrain (bought used and had way more wear & tear than I expected). I now watch for a sale on a new group or parts
- I had excellent help from a neighborhood bike nut who helped me with the 1st build. I would not have attempted the build without him. We used a shop for headset and BB installation.
- The commuter was cheaper than new as I held onto usable parts from the road bike as I upgraded and used them for much of the build.
- Patience, sales and closeouts and more patience are your friends. As is qbike.com (on line price comparisons). Ebay auctions can be your enemy, although they do offer entertainment and frustration when it is too dark/cold/wet to ride.
- Too many people on ebay over-estimate what a bike frame or part is worth, what is a reasonable bid (vs. NOS or retail), or the meaning of "almost new".
- Make some purchases at local shops - you want them to be around when you need them.
- Buying new would have been much faster and probably less trouble. I've held off making a full accounting on what I spent on pieces, parts, etc., as I don't really want to know the truth and don't want that info where my wife might find it!
The experience I gained has been invaluable as I can do most of my own maintenance now (have not attempted wheels and hubs yet).
An approach for someone starting out is either get a basic tourer and learn from that what you really want (and are willing to do), or find a bike with an excellent frame and upgrade parts as necessary as they wear out and only if you've decided the bike is a keeper. A bike shop gets a much better deal on a complete bike than most individuals can obtain.