Well, that's a multi-part question.
1) I had both faulty CPU and Power Driver boards which I replaced with Rotten Dog. I don't really count this as these were not mods, but necessary repairs.
2) Parts & supplies: misc repairs, hardware, new rubbers, new flippers, cleaning stuff, paint, etc. I would guess about $400-$500
3) Purchased Mods: Vinyl wrap, LED's, Key Starter. $300-$400
4) DIY Mods: very little as most of these are my own design, self print, and self made.
5) My latest expenses: PinSound & PIN2DMD, about $550
Plus all of the above was supplemented by a few hundred bucks that I made selling my mods to many at very reasonable price points. Have I spent more on the machine that it is worth, sure. However, this is my very first pin and I've used it as a learning experience. I have performed all my own repairs and mods with the help of this forum over the last year, and have loved every minute of it. Also, I never see myself departing with this machine.
If I was starting over with a solid machine (I now know better what to look for), I would say you are probably looking at $2,500 or so to get into a nice Getaway, $300 for LED conversion with adds, then it's up to you on anything you want to spend above that along with any DIY mods. I know others in this forum have much less on theirs, and I also know others have much more. Of course, you are always welcome to find one that already has most everything you want, and pay a premium price for it in exchange for not having to do much/any work to it, but where's the fun in that?