I have never built up a bike, but I'm thinking about it as a fun project. Seems like there are often good deals on parts, especially this time of year. You probably have to be somewhat flexible on what will end up on the bike, or at least how long it will take to get all the parts, but my guess is that you can probably do okay by getting some stuff on sale and even some stuff used. But, like I said, that's just a hunch. And, of course, it only makes sense if you want the experience of assembling the bike.