Well, I've broken off my second 5-40 tap in cast iron (model steam
engine). One I got out with an extractor - the second one I've
buggered up so much my only hope is to drill it out.

I've read a number of posts about drilling them out with carbide bits.
When I look in KBC, Wholesale Tool, etc., I see solid carbide jobber
bits for 10 bucks or so in size 39. Will one of these do it? Because
I also see a "square die" carbide bit that specifically mentions
drilling out taps - but it's $35...

If I need the $35 bit, so be it. But, if a regular carbide jobber bit
will do it, I would obviously rather go that way.

TIA,
Wally