Chances of a car under 10yrs old these days falling into the banger-nomics and require welding is highly unlikely.
Inlands, maybe.
An E46 3 series over here pretty much is guaranteed to require welding. Though after a quick googling it’s slightly older than 10 years, so they might’ve fixed that on subsequent models – but here where i live, a mile away from the sea, cars rust. Quickly indeed. Our SEAT MY19 was brown underneath within half a year. Of course, not rusted through, but it’s just a matter of time.
And you’re right, Dacias etc can be had cheaper than they’re offered on the scheme – but that’s because they’re exceptionally cheap to buy new.
More importantly though, it not just depends on your monetary situation, but also the kind of injury. Many people require certain things, like us for example needing “the right seat” for my wife. A worn seat is simply out of the question, indeed many new seats don’t work for her either (that’s why we had to go for a “hot hatch”, because the seat locks her in).
On top, many people require adaptations. A lift can double or even triple the price/value of a banger.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.