I started a list of items on a spread sheet. I list each item that I need along with approximate time it will take and price it will cost. I do not want to keep track of receipts again. I did that when I built my S-10 daily driver. I kept track of every nut, bolt, primer, paint, screw, light-bulb, etc. I had discovered that any budget is off by a factor of 3-4.
I now use the spread sheet for cool things like figuring out vehicle balance, steering geometry, suspension geometry and vehicle mass. I no longer want to know how much I spent, or it would ruin the hobby.