Well... my bike is still in pieces .. but with the price of the bike ($650) and the parts up to now I'm in with around $2200 on a bike that when in perfect collector condition is worth around $3000..
The thing is, even if you are reusing old parts you still have to put work and stuff in/on/over it to make it work again.
And probably you are missing tools for the job so new tools has to be bought (yes you can't count that in to the total, but nevertheless it's something that is needed)
Heck, even welding material costs as you use it, Sandpaper costs, cutting wheels costs, nothing is free or cheap when building/restoring stuff, it can just be expensive or less expensive.
But the the costs are quite irrelevant when it comes to a passion, you take both time and money to do what you want, sometimes you have very little of on or the other or both. But in the end, A lot of money and time have been put in to your bike, sadly the time part doesn't show as much as you would like. (After have been cutting and wetsanding my brake and clutch levers for hours and hours it still looks like it's factory, nothing special, but still.. a lot of time and it made me pleased when finished. (and yes less expensive but still some money went in to it)
Bah, rambling of a madman, My point is. NEVER think that your bike/car/boat will be a cheap build. Forget about the money, make it the way you want it to be! Money comes money goes but glory remains!