As part of another project i've been thinking of making a "ghetto" hot end of all metal design.
Sorry for the *really* bad design pic, i usually draw everything on paper and not on computer and didn't feel like making a 3D model for this.

So i've been thinking of making a ghetto style hot end.

Minimal BOM is:
1x40W Heater cartridge
1xThermistor
3mm ID/5mm OD SS Pipe ~15-20cm
5xM5 nut
1xM6 extension nut
1xM6 bolt/piece of threaded rod
1xM6 nut (cartridge mount)
~10xM5 washer
~10xM5 fender washer
1x40mm fan for heatsink cooling
1xSmall piece of fiberglass insulation (optional/prototyping, not certain yet of requirement)
1xSmall piece of kapton tape (optional)
1xPrinted fan duct & mount (after first prototype will know exact dimension and model it)

Tools required:
MIG/MAG Welder
Drill/Bench drill
Dremel
Wrenches
Angle grinder etc.
Listed in picture

Cost of making this hotend, first piece (larger quantities minimum purchase):
SS Pipe 1meter: ~5€ max
Heater cartridge: 2-5€ (single piece)
Nuts+washers+bolts: 2€ MAX
40mm fan: 1€? 2€?
Fiberglass insulation: If you don't got, don't bother purchasing, tho you can get from various sources small pieces for few euros with tape, automotive exhaust header style was my thinking
Kapton tape: To secure wiring etc. you can also use aluminium tape, SS zip tie or whatever
Thermistor: 0.5€?

Shipping costs etc. will be the greater cost, and just making a single one raises the cost. So parts are best acquired as part of other orders etc.

My cost for the initial one will be something like:
SS Pipe x2 under 10€
10pack of heater cartridges 15€
pack of thermistors ~5€
Nuts & Bolts: 5€
But those will be enough to make 10x hot ends with single heater cartride (i'd like 2 with lower voltage for more even heat distribution if that matters at all) and a bunch of nozzles
Total cost is then: 35€ + probably 5hrs of shop time for the pack of 10
+ micro drill bits i had to order but obviously i should have these in any case

I'm thinking the first one will take me 1-2hrs while fiddling around with exact dimensions etc.
Further units will take like 30mins to make. Hardest to make is the nozzles due to so much drilling and precise work. The slowest piece to do is the threading on the SS pipe.
To build this quicker one could weld in most of things, if non removable pot then only thread required is ~20mm on top or less.

Any obvious issues?
I designed it with that long nozzle piece so i can drill it out for larger diameter - Does it make sense to have a larger melting pot, or should the melting area be kept small and neat? Perhaps even going below filament diameter BEFORE the actual nozzle?

Benefits of this for me at least is that i can make 0.15mm nozzle
Another benefit is that i can design the preheat distance for VERY fast printing, and the mount being with nuts i can secure it tightly on the mounting piece.
One the first one for testing i can't obviously have the extra chamfer on top end so i can dissassemble it almost fully still if i need to make the heatsink taller.
Also this is trivial (and designed for) dual heater cartridge so reaching polycarbonate temps on high speed is not the very least of an issue, then again 40W properly mounted is strong enough to make it non issue to begin with.
Further, you can remove either the full pot OR just the nozzle.

I'm also hoping that after drilling out the hole for heater cartridge it's a very snug fit, so no grub screw required.

Drawback: Cold pressed mild steel + SS is heavy, but on the plus side, the heat capacity of those is LARGE if you are targeting ultra high speed.
Ofc, not everyone can make these at home since welding is required and preferrably a proper angle grinder which i would not recommend anyone to use at home due to fire hazard.

Further development could be doing the heatsink from aluminium if i acquire (or better yet: MAKE) a lathe and find properly cheap aluminium stock

What is the cheapest all metal hot end on the market right now?