Cheap? Carbide Countersink?

[old mart]

How about this type, using common, easy to get tips : https://www.ebay.co.uk/itm/Drill-Too....c100706.m4781
APMT 11 and APKT11 from China in a polished grade for aluminium costs peanuts for 10 and there are 20 cutting edges.

[nickel-city-fab]

Could you use chamfering end mills to do the job? 90 deg and carbide, easy.

[PStechPaul]

You can get a diamond countersink for about $15:

https://www.ebay.com/itm/Electroplated-Diamond-Conical-Countersink-Drill-Bit-Grinding-Glass-Hole-Arris/162649183980?hash=item25dea596ec:rk:15:pf:0&var

Or a Sandvik for $1200!

https://www.amazon.com/Countersink-Flute-Polycrystalline-Diamond-Uncoated/dp/B07DR4WMPF/ref=sr_1_15?s=industrial&ie=UTF8&qid=1543969447&sr=1-15&keywords=diamond

[doctor demo]

Madman, check your private msg. box.

Steve