You can easily build one game for 10K or less.
Yourself. With a massive skill set, and a huge personal time expense that you value at $0. Here are some of the resources you need to build an entire machine yourself:
1. Woodworking, cabinet construction, painting/decaling. Or you can buy a fresh new prebuilt cabinet; VirtuaPin makes them, but it'll run you nearly $1K at the moment.
2. Game design and theory. You need to know not only how to create a physical layout that incorporates all desired features with the appropriate amount of engagement and flow, but how to lay out rules that keep players interested. I can't speak for all Big Whales(tm), but if I was dropping ten grand (or, y'know, a hundred) on a one-off pinball machine, I would want a genuinely fun experience that I can share with my friends.
3. Creation of printed playfield. For some of us, this is a struggle that will have to be outsourced - looking at myself in the mirror on this one. This particular skill, however, is one that GWJ is known to have, and indeed it's quite valuable knowledge - setting aside the repro situation that went sour.
4. Assembly of playfield and cabinet. Arguably one of the easier tasks, but it still requires a lot of attention to the designer's (your) intentions and making sure things fit properly, especially those elements that be arranged at different angles but need to fit around other components. Flipper baseplates and pop bumper spoon switches are well-known offenders.
5. Electrical wiring. High-voltage switching comes with many reliability pitfalls, and you need to design your wiring system in a way that reduces or eliminates interference, usually also allowing for future maintenance down the road. A high-dollar investor will want to know his game will not become an unmaintainable mess.
6. Electronics systems design. Wiring alone is not enough; one end goes to playfield devices, but the other end is going to plug into something complex that controls everything. There are off-the-shelf controller solutions that can do all this work, but they'll run you several hundred dollars at least, if not another thousand for a whole fleet of electronics. If you're an exceptionally insane person who loves the feeling of doing everything from scratch and is more than likely somewhere on the autism spectrum, you could design your entire electronic control system from scratch on custom boards - which requires its own set of skills. You can't get out of heavy computer use if you're doing this, unless you can do PCB fab on pencil and paper and don't plan to use any silicon in your design. Which is unlikely.
7. Artistic talents. There is a stereotype that people who are good at computer programming aren't very good at art. Plenty of exceptions exist, people who are brilliant at both. But as someone with very little skill in drawing people, I am outsourcing my current build's art, just as I had to do with the cabinet art on my first one. Artwork is very much an integral part of the pinball experience; it is, after all, the first thing that attracts players to the game. And you definitely want the best art you can get if you want TPB to be "pimped out." Good artists do not work for free and shouldn't be asked to do so.
8. Sound and music composition. While your "licensed" game might offer you a fair amount of music thanks to original soundtracks, it won't get you all the way as far as a game goes. As a player, I expect audio feedback from every shot or target, otherwise the game feels dead to play. Not all sound effects make sense to rip directly from a TV show; it's going to take some custom work. Music is very much its own art, and good musicians and sound engineers are not free either. Lacking my own musical talent, my current project outsources its music to a good friend who has years of experience both operating sound equipment for bands and playing it himself. And no, it's not free - I paid him my Firepower in exchange for it.
9. Computer programming. There are software solutions for clicking together a game without needing to write actual code, but there are limits to how much you can do with such a system. A pimped-out game definitely needs custom code that pulls together the physical and the visual, and keeps everything smooth and pleasant to look at.
There's probably a lot more, but for a garage build, this is what I could think of off the top of my head. Like I said, it can be done... but it's hard, much harder than it might seem, and most of us aren't given a budget for free. If you don't have every single one of these skills, you need to seek out others who do (as you seem to be doing). For a $10K budget per game, there's no way you'll be able to hire anyone with marketable skills to design and build the games, and even the original goal is stretching it thin. That's not even counting the legal issues of paying contractors to design and build something you don't have a license for.