Here is stage 1 of my latest project: a cheap workshop dust cyclone that SUCKS :-)
Stage 2 is available at this link.
I recommend you to start out with this one, though!

And this is what you need:

• a workshop vacuum to create suction
• a 3D printer that can do 18cm object height
• a 30 liters hobbock with 33cm diameter (I bought this one) for 20€ - if you buy two, you will have one left for stage 2 with FOUR mini cyclones to separate out even finer dust.
• a metal nibbler or a very good metal saw (if you use a metal hobbock). Nibblers can be had for less than 15€ at Aliexpress.
• some DN75 tube from your local hardware shop or an adapter from your suction system to DN75. I chose DN75 because it is big enough for most applications and adaptors to other diameters can be had dead cheap.
• 10x screws with countersunk head 3mm x 10mm
• some silicone or flexible glue to get things airtight
• about 90g of PLA or ABS
• a metal file
• 1.5mm metal drill
• a marking pen

First you print out the intake and vent parts. I recommend using a brim on them. Once you have the vent finished remove the FDM support with a knife, hold it against he hobbock and use it as template to draw the intake hole outline on the hobbock. Then use the saw or (preferably) a nibbler to cut out the hole. Try not to bend the metal.
Use the metal file to remove grates from the opening.
Mark all screw holes with the marker. I recommend to mark them with a nail tip and a smal hammer as well; this makes drilling a lot easier.
Use the 1.5mm drill to prime all screw holes.
Draw a 2mm wide line of silicone or glue on the intake part around the intake hole and fix it to the hobbock with the screws.
Put the counter caps over the screw tips on the inside of the hobbock.

Mark the center of the top lid of the hobbock and draw an 81mm (diameter) circle around it. Use the nibbler to cut the shape out. To fix the vent part onto that hole proceed the same way as with the intake.

Now you have a dust cyclone that can be fitted with standard DN75 tubes or adaptors and it cost you less than 25€ - or less than 20€ if you bought more than one hobbock.

In my tests, the cyclone as shown absorbed considerably more than 90% of the debris it takes in as it is. I have finished development on a second stage for fine dust that catches at least another 90% of what is left. Stage two is a little more costly but still a lot cheaper than any comparable, commercially available solution.