This build is intended to demonstrate that it is possible to have a stunning looking 6S ready, Floss 2.1 6" quad, and complete the build for under $200 (USD). Ended up at $185 actual cost, and the performance this thing can unleash on 5S is shockingly good.
With 2018 Black Friday sales, I've been able to replicate this build using F60 ProII's for $225

The custom parts include: 4mm (pair of glued 2mm plates) base plate, custom RIT dyed Phoenix3D Canopy with Silver Spray Paint, and modifications to accept MMCX Antennas. If you want to run an MMCX AXII antenna with this canopy, just email Chris @ Phx3D and he'll set you up with the customized canopy for this setup.

The cost savings are in the combined FC/VTX (F4 V5), the FlySky X6B Receiver, and Sunrise 4-in-1 ESC - but these have performed brilliantly. IBUS over the much more reliable X6B receiver is actually excellent (compared to D16 SBUS), and with supplementary capacitors the F4V5 FC/OSD/VTX works brilliantly and is quite stable.

While the RK5051 props are what inspired the color scheme for this build, I actually daily drive this thing with DAL T5046C's or GF5149F's. The V2 Cyclones are the most predictable and consistent feeling props across all speeds, while the 5149's are amazing for high speed control and cornering grip. The inherent efficiency of this setup means I can run these props and still see much better battery life during races.

This is the best quad I have in terms of race performance, and with this particular one I've advanced from being the literal last place finisher at local events to lurking around the semifinal rounds in terms of pace - so if you're looking to build a competitive setup it's hard to justify spending a lot more than this.

In terms of flight efficiency, even on a 4S 1300mAh pack, I was able to run four laps of Bryan Polk's BMPR2 track {a long track, about 30s / lap track for NytFury and Freefall} using only 950mAh. Tall stator and lower KV go a long way, since I'm not good enough to need the top end.

As far as the basic electronics stack - I actually would highly recommend this for somebody looking to achieve extreme performance on a tight budget:
Furibee F4V5 FC/VTX // ZMR 30A 6S 4-in-1 ESC // RCX LS2207 1700KV Motors // Floss 2.1 Frame
With a 1000uF 35V cap on the VBAT rail and a 220uF 25V cap on the 5V rail, everything stays clean and well behaved. Extreme efficiency is possible using a 5S battery on 6", and extreme performance with good disc unloading is possible with 6S batteries and 5" props.