Tough question, which depends on which car, which level of pre-assembly you choose, what you want to do to it that makes it more custom to your specific vision for the car. Some of us start from scratch, so welders, metal saws, grinders, hole saws, die-grinders, drills and bits, a good drill press, files, clamps, angles and good measuring tools, taps & dies, etc. So that's just for a bare space-frame (I would consider a build-table as a "special tool" to some degree) with no shear panels, interior, or body. If all of that is already completed, and you just want to add shear panels or go full monocoque, then a sheet-metal brake, metal shear, Cleco tools &fasteners, Rivnut tools and fasteners, and a pneumatic rivet gun are minimal starts. And I haven't touched electrical wiring needs, bodywork tools, hoists, etc.
I use a 30-ton press frequently in this hobby for one thing or another, and just when I think I can get rid of it (takes a lot of space), I find a need for it again as I work on perhaps another project. Some folks will purchase a lathe or mill to get what they need out of the project.
It can go on and on, which means you'll need to candidly assess your fabrication skill level, what you're willing to farm out for machine work or for others to do for you, time you want dedicate to the build, and go from there. A lot of the "tools" I've purchased or fabricated are tools I may never ever use again unless I build another car, and that is less and less likely. I wouldn't say I've spent as much on tooling as on the car, but it could be a possibility depending on which end of the build spectrum your at.
Metric and SAE wrenches/sockets 8mm-24mm, 1/4"-1". Extensions, Get 1/4", 3/8", 1/2" drives.
Metric and SAE allen head wrenches/sockets and buy the 1/4" if not in the set.
Adjustable wrenches. Screwdriver set.
Angle grinder x2, die grinder
Cordless drill, good 1/2" drill, drill press (spend money here)
Vise (spend money here), chop saw, jigsaw, circular saw, Dremel.
Belt sander, grinder.
Consumables: (cheaper stuff is fine- you will not care about breaking them and buying more- and all bits get tossed) drill bits-Warrior from HF is fine-can buy 2 sets for $25, step bits, flap wheel, wire wheels.
Astro 1442: I used it a dozen times- can get by without, more fun than useful for my build.
If you plan on building one of the space frame "kits" I personally would add a powered caulk gun as well. There is quite a bit of sticking panels down and seam sealing. While you *can* do it with a hand caulk gun you're going to end up with one hell of a sore hand (or fail like me and end with a broken gun). Bit like you *can* hand rivet it but get a rivet gun!
I tried the air ones and they were crap, just leaked air so in the end I got an electric one, a Ryobi ONE+ P310G which is awesome.