Your frustration is not unusual.
When dealing with operators, my choice has always been to take the 'cheap' price, so long as you were getting a complete, or nearly complete game.
On the odd chance they might have good parts a game needs that are rare,like plastics, or a ramp, or something, you might make an exception - years ago, I bought an IJ from an operator who parted out another one - and I got all his leftover parts for a very sweet deal along with the 1st machine - and needed some of the parts.
If the operator wants $100 to go through the game and get it working, I'd say he probably plans to have his tech spend 20 minutes on the game with a bottle of windex, wildcat, a couple rags, and *maybe* change out some burnt bulbs, or a rubber or two. Maybe swap in a board, if one isn't working completely - but still, you're not getting $100 worth of value for your $100.
Now, this is gonna seem harsh, and maybe it should sound harsh - but it's real, so I hope you won't take offense.
If you aren't capable/willing to fix a project game, don't buy from an operator. Don't buy from eBay. Buy from a fellow collector who you can go play the crap out of the game, inspect things, ask questions, and pay the premium price such a game has attached to it. Most ops consider a game that sorta lights up, sorta plays, and definitely takes quarters, to be 'working completely'. Their interest in pinball is different than yours and mine. They don't sweat stuff that we sweat.
Ops don't want people to kick tires. They don't want people who ask questions. Every operator knows several people who want to buy games as-is for good, cash prices. If you want to be that guy, don't ask questions. Pull up with your truck, give a very quick inspection to make sure the game is complete, no burned spots in the game, etc, hand cash, load game, leave. Call back again when you have more $$ to spend, not when you find a burnt connector, or a slight issue. That's to be expected.
Now, the bright side?
I've learned at least 85% of what I know about pinball from fixing games from these operators, or very similar sources. A broken game, or a part working game, is a great way to learn. Turn it into an opportunity! I'll take a look at your linked thread, and see if I can offer any advice.