I challenged myself to build a 3" quad for <= £100.
Ordered everything from Banggood, could probably get things cheaper elsewhere.
Prices may seem a little high in the list as BG do discounts on orders of >3 of the same item,
My order came to a price of £98.43, and I am leaving the remaining £1.57 to cover small parts I already had
(voltage regulator, battery strap and heatshrink)

The build is now done! It was a little more fiddly to put together than I'm used to, but it's working and flies great.
The dry weight is 94g, 168g with a 3s 850mah battery; according to the specs of the motors, this should give me a 4:1 twr. (max 170g pull per motor with a 3020 prop)
I'm very happy with how it flies on betaflight 2.9.0, which the cc3d can run at 2.66khz.

A few things to note:
• Yes, I know, XT60s are oversized for this build. It's what I had, I will be replacing it with an xt30 connector once I get some.
• The frame's motor holes are not spaced for 1104 motors. I had to dremel inwards to fit them.
• The camera mount included with the frame is sized to fit over a standard camera lens, so it was not used with this micro camera.
• The receiver was marked as an Airwolf rx f702 board, rather than the f801 I expected. It works fine in ppm mode after de-pinning.
• I opted to use a sleeved dipole on the vtx as it's lighter, less likely to snag and be damaged in a crash, and was no cost to me as I extracted it from the rubber duck antenna the vtx came with.
• Removing the sma connector from the vtx was super easy - flow some of your own solder into each solder point, then flow some solder onto the connector itself and heat the whole thing with your iron until it slides off with a gentle push. If you have to use force, you're likely ripping pads off.
• I chose to use a wiring harness for power distribution, which I made from 18awg wire. It may have been lighter to use a small pdb or even a pdb/fc combo board, but this would have pushed the cost over my £100 limit.
• The 5v regulator was pulled from a dead ESC. I'm sure you could buy a similar chip for very cheap, which wouldn't push the build over £100.
• Don't throw away these 3020 props when one blade breaks off! Because they mount with 2 screws, you can reuse the single blades mounted with one screw each to make folding props. You just need to remove the rest of the hub.
• I made the battery strap from some stick-on strips of velcro and electrical tape. The Electrical tape seems to work well as a rubbery backing, which stops the battery from sliding out as easily.
• The camera mount consists of 2 nylon screws and nuts, and a piece of credit card bent to shape. It fits in the conveniently (otherwise unused) holes in the side plates.
• These motors are annoying to solder. The pvc insulation prefers to stretch rather than strip, and you also have to scrape the enamel off the single strand wires before you can solder to them. Make sure you have proper tools to make this easier.