the absolute best way is to buy the cast-me-off rig. When Rick Pewe got rid of his desert runner truck, he sold it for literally pennies on the dollar (IIRC, 20k) - which isn't bad for a top-of-the-line sorted desert truck. Then you learn without the curve - and you don't have to ask the experts... that line, ummm, a cautionary tale - I have a 455 Buick motor that's been at a machine shop for 2 years, when you have to rely on others; you may find they can't or won't come through. Or, my Fiat took 3 years to get the wiring harness done. Since it took 3 years, I've built: a 1983 4x4 diesel pickup with turbo, paint, axles, interior, a 1975 Corvette with roll cage, new motor, new trans, new rear differential, updated/upgraded/badass suspension, and a myriad of other projects. Point is the Fiat would be done had I been able to focus on it. Now I won't pick it up until the FJ40 is done (a year, at least).
There are so many ways for a project to be derailed that my advice remains, buy the best vehicle you can possibly afford - run, fix, update, and run some more. When that vehicle is done, then do a grandma-fresh (perfect condition) vehicle and update it, after that one is done, then do a race car. Once you've done those.... build the 4x4 of your dreams - a lot of the build is knowing what expert to use, what parts work, who to buy parts from, and not buying parts you won't end up using.