I built (and still building) my Thunderbird with no funds at all from my paycheck. I have to be very creative at times, but in the end, it's paid off. I got a Mountaineer GT40-P engine with less than 15,xxx miles on it for $125.00. Sold the engine I was using for $550.00. Profit for more parts. Sold my polished Explorer intake for enough to buy a "cheap" tubular GT-40. I polished it and sold it for enough to buy the 'used on a dyno only" Trick Flow Street heat intake and 70mm t-body and new, in the package, Summit 24# injectors. I shop around a lot on Ebay as well. I saw a guy who had a polished 70mm t-body and spacer for the right price. I sold the non-polished 70 for enough to buy them and had about $25.00 left over. Lots of trading, and selling of my old parts. I also hit up the salvage yards looking for cool parts. I get them cheap, and sell them for a profit to make funds for the car. I've built the whole car that way. Nearly every part has been replaced.
Like stated above, buy low, sell high....so to speak. I do that a lot, but sell at a price that's fair for others, yet puts a little in my pocket. Patience and keeping your eyes open. Also, after a while, I grew to love the thrill of the hunt, and, knowing I have no paycheck money in it.