Your budget is not the purchase price
The car is only one line item. Transport, registration, fluids, tires, brakes, battery, tools, workspace, and outside labor all compete for the same money.
Create three separate reserves
Keep an immediate-maintenance reserve, a repair reserve, and a modification budget. Combining them encourages you to spend reliability money on cosmetic or performance parts.
Assume the first estimate is incomplete
Every unfamiliar project contains hidden work. Add a contingency percentage before buying, not after the car is already in your driveway.
Price your own limitations honestly
Time, storage, transportation, experience, and access to tools have financial value. A repair that costs little in parts can still stall a project for months.
Build in stages
Stage zero establishes a reliable baseline. Stage one improves safety and feedback. Only then should later stages add power or major cosmetic changes.
Know the exit condition
Set a maximum total investment and define which discoveries would make you walk away. Quitting a bad project early is sometimes the most profitable repair.
Final recommendation
The most useful next step is not reading another generic opinion. Define the exact configuration you want, establish the total budget, and inspect a real example using a repeatable process.