Bicycle Mechanics - STIs on an old 6 speed Peugeot!

My first venture into forums so thanks for reading! I've an old Peugeot steel framed 12 speed bike - the shifters are on the down tube - it also has an old maillard hub/cassette (which I think will need to go alas).
I want to upgrade this to an 8 speed with STIs, preferrably Campy but not that bothered (there's other campy stuff on the bike). I've read that this can be done using a 'hyperglide' hub so that the frame does not need to be 'sprung' but in reality I really don't know where to start. Does anyone have any ideas please? I need to keep the cost fairly low!

I'd try the vintage board.

A French bike that old might have some funky threading and sizes.

You frame is spaced 126 mm and 8-speed anything requires 130 mm so you will have to "spring" the frame to get a new wheel in. You can either struggle a bit each time or have the frame "cold set" (permanantly reset) to make it easy. And yes, your Maillard hub won't accept any of the newer cassettes.

BTW "STI" and "Hyperglide" are Shimano trade names. Campy calls their brifters "Ergo". The two makes' hubs and cassettes won't interchange either.

Unless you already have 8-speed brifters, don't bother with 8 and go all the way to 9 or 10. Eight speed is obsolete and both Shimano and, particularly Campy, 8-speed components are getting hard to find.

This could be a very expensive upgrade, particularly if, as RG noted, the bike is old enough to have "French" threading.

Anything you do with STI is by definition not going to be "low-cost" just by having to pay $100+ for some shifters. You'll need another rear wheel (& front if you want it to match), cassette, chain, and front and rear derailleur at the least. For 8s you'd probably want to upgrade your crank, too.

Fot the drivetrain, you'll need to match the rear hub and cassette with the shifters/derailleurs. Campy and Shimano don't mix very well in the STI/Ergo world.

There have been several threads in C&V about doing this, and many opt to on frames they love. The general consensus is that to do it right without having donated (or close to it) parts will run you about $400. Good pics of upgrades in one of the threads over there. Don't remember the title, tho.

If the bike has French threads, they would be on the headset, bottom bracket and perhaps the pedals, so they shouldn't be a problem.