Look at the price of the whole bike with your preferred or dream frame because that is what it is going to cost you at the very least if you don't waste your money on junk or unwanted components on the way. If that is out of budget then think otherwise and look elsewhere.
Other options that might be cheaper is looking for a secondhand frame to build up, either with new bits or with carefully selected used gear. Joining the right club where people will offer you stuff that they're changing is not a bad way to go either, although you have to take what is offered and accept that it won't be the latest fad. Beggars can't be choosers holds true in this respect.
If you know what you want and know enough about the subject to trust your judgement buying secondhand, either a complete bike or components may be a suitable option.
I have frequently thought the way you are thinking but I have never made the sums add up. It will always be cheaper to get what you want/can afford straight from the start.
(FWIW I am a cheapskate; I have a few clubmates who have always passed me on nice stuff that just happens to be obsolete and not worth them selling. I can recommend this route to cycling pleasure if you can't afford your dreams!)