It's not really dangerous to drive with a bad CV joint but it's not a very good idea either.
If the bad CV joint gets worse enough it can break and then leave you stranded on the side of the road and possibly in rare cases the CV joint might cause a bad accident.
But usually the bad CV joint just breaks and leaves you stranded where you're unable to drive the vehicle any further.
If you hear any roaring or grinding noises coming from the CV joint or clunks you should get the CV joints replaced before they break.
If the car isn't worth much and you plan to replace it anyway then driving with the bad CV joint is not that bad but still anything could happen and if it it breaks you're gonna need towed.