Yes, it really was that cheap. It's also probably the best quad I own.

This is definitely a black friday budget build, with some clearance items, but I'm probably going to copy it at higher cost because it's so good.

The budget magic here is a combination of comically cheap prices for premium parts, and not running anything extra beyond that.

Motors came from RDQ Clearance at less than $11 each. I talk a fair bit of trash about TMotor F-Series pricing, but when they're cheap, I will choose those every time. The V3 Pro versions in 2150KV are a truly amazing motor to run, and arguably the most flexible setup around, because this allows for 4S, 5S, and 6S batteries with some variations in propellers.
Frame is a FPV Flight-Club Neutron-R. Same frame I've loved since the first one, I now own a dozen of these. The MaydayFPV designed canopy and Purple color has simply become the signature look for my quads, and this one is no different.
Stack is a HeliNation Talon F7 Fusion with Gigawatt V2. With the BlackFriday 20% off, this was a competitively priced stack, and arguably the most gucci set of electronics I have ever put on a race quad. Sensor fusion is amazing, F7 ease of use is phenomenal, and I know that ESC is ready to party on 4S/5S/6S with minimal changes to settings via the firmware (I run everything at 48kHz PWM, 23° timing, 0.25 rampup power, and demag comp on low). The overall tune is really straightforward, I have previously run BF4.3 with sliders at: Master 0.9, PD Balance 1.3, P&D Gain 1.3, and FF 2.0, using DMinGain of 50 and DMinAdvance of 100. The sensor fusion allows me to disable gyro lowpass filtering, run very aggressive DTerm DLPF filtering (biquad at 1.8 - this is aggressive, not recommended), otherwise running the tuning notes suggestions for dynamic notch and enabling yaw LPF.
Tune is the Tehllama Preset, that will become available with Betaflight 4.3 and the updated configurator (Thanks Limon!). The 4S/5S/6S 2150KV 2207 preset was built specifically for this quad, although I have tested it on a lot of variations on this same theme. It should work for that entire battery range and use the profile auto-select functionality, but be advised that it is intended to be ran wide open even on 6S batteries, so be prepared to use the transmitter to throttle limit.
FPV Gear is another budget set of choices. Foxeer's ToothlessNano 1.7mm was $20 from HeliNation, and is a brilliant camera. I don't see it as an improvement over the Predator V4/V5 that I usually run, but both are extremely nice cameras. I've given up and stapped running budget cameras, because I can reliably get such good performance out of cheap builds that it's worth paying extra to see where I'm going, otherwise I find myself constantly 'outrunning my headlights'.
The VTX is an AKK Race VTX, because $10 VTX does what I need it to. Finally, Foxeer Lollipop V3, again, on sale, but those are absolutely my favorite for ruggedness. The FC has a built-in VTX switch, making that entire thing easy.
Props are part of how I manage the very high KV - lower pitch is the answer. Gemfan 51433, HQ 5.1x3.6x3, and DAL T5040C props all work well on 6S setups. For 5S 1100mAh Black Series packs, this thing is a true animal. GF 51466 and TM5146 props are my favorite in that configuration. On 4S, I like the same 51466 props, and can use up my 51499 and DAL T5050C props as well.
Overall, the higher voltage lower pitch props give up a small amount of efficiency but return massive amounts of stability and performance in tight turns/moves providing much better lap to lap consistency. I find the sweet spot to be 5S on these motors as I can run them without any output limiting (cap transmitter at 94%, which allows the PID controller and mixer to still ask 100% power from a motor or two). On 6S, I usually limit to 82-86%, which is meaningfully more power on offer and probably contributes to the reduction in efficiency, but I am slightly faster and it feels more consistently locked in.
Batteries in this case are all CNHL units because price. The weight and performance of the black series is phenomenal, although I still use a lot of the older 100C G+ (White Series) packs because of insane value that I'm willing to punish them hard. There are some other oddball batteries I enjoy using, including the Talon 5S 900mAh packs, which are super-light, as well as the CNHL 6S 1000mAh Ministars, which are also phenomenal specific output packs.

My best builds are not the planned builds,

This just reacted to sales, an turned into the best flying quad I own.
I have probably spent too much money seeing just how cheaply I can build a good racing quadcopter, but can make the results consistently pretty good...
This partially breaks from that trend, because this is what I would build without any budget considerations. You can substitute frames (FlyFive33 SwitchbackPro Hybrid, Pyrodrone F3LiX, and FPV FlightClub Neutron-R Hybrid StretchX are my favorite choices). Any other motor in the same size/KV range is going to perform brilliantly, and there are other ways to get the performance of this stack, but the Talon version is both the prettiest and best value in this case.
Running nicer RC/FPV electronics at your discretion is nice - I'd keep the antenna no matter what, and if you want to run Tracer/Ghost/eLRS/CRSF that's awesome, but my XM+ running D16 8ch still turns in 9ms framerates somewhat consistently.
Short answer is that you'd be hard pressed to come up with a completey better build than this - some marginal gains that cost a fair bit are possible, but I'd rather have a matching fleet of these than something slightly nicer.
My all-in price of $185 is a black friday fluke, and required buying other stuff to hit minimum order quantities to ship free. This ignores the price of consumables (props, batteries), and doesn't cover spares.