babie_lato I know you're looking to restore/build the mixte yourself, but given what you're willing to spend have you looked around the various restoration shops? Many of these bikes can be had for a decent price, are mostly nicer bikes and professionally restored. I follow these on instagram and like what they post:

https://www.dynamocyclerepairs.com/
https://www.damsko.co/
https://ambikeco.com/
https://www.instagram.com/frenchwheels/
https://www.instagram.com/galaxybikes/?hl=en
https://vintageveloberlin.de/

Not what you came here for, I know, but if the search doesn't yield decent results soon and you just want to pull the trigger on something it's worth having a look at those.

Also, I understand the Peugeot hesitations, but as has been said here, they made some nice mixtes, they just aren't as common. And the low end ones are actually also pretty nice when you do away with a lot of the steel components and wheels and swap them for alloy. If you were to just start with a frame it could be worth it. Here's one I recently totally overhauled for my friend. Almost all of the entry level steel bits were replaced with nicer, but mostly period appropriate, alloy components and it's quite light and a beautiful ride. Granted, it being single speed did a lot for the weight.