cheap sleeps: FR is not noted for that. Most young people will have heard of places named hoStels=multi bed rooms, often with kitchen/self catering and common space.

On nearly all well-known hotelbookingsites (like booking) you can also find them-just click on cheapest first. There is a special ditto site for them: hostelworld. But FR is not really noted for very low prices-if you can find such a place, reckon on prices around 20€/bed/night.

ALT: a site as couchsurfing lists people offering cheap or free sleeps-just a place in their home, crash-pad as it is called in USA-english, but you have to make all the contacts by yourself.

The final cheap sleep: spending the night without a bed in airport or even train station: site sleeping inairports gives descriptions. But Brd hardly has a sizeable airport.

When IR started long ago: then there were plenty of overnight trains, without any expensive extra REServation. But that is no more.

On this site we-alas- see very very few young people who react as helper after their travels or checking like you ask for help on local knowledge. Its mostly young newbees who all ask the very same (and after a while also very boring) questions. I spend a night in Brdx indeed on my last IR in sept ́21, but did not really see too much of that city.

I’ll second the above - provided you have the use of a computer/smartphone you’ll be able to look up hostels in Bordeaux without too much difficulty. AirBnB can also sometimes have a few listings that are a bit cheaper than standard hotel prices. Bordeaux isn’t the cheapest of French cities though, and in many respects it’s quite an affluent, bourgeois sort of place (at least in the central area where all the major points of interest are); it’s known primarily for its wine, gastronomy, and genteel 18th century cityscape.