You've received some good advice above from some of the best on the forums. I personally would not drive this car except in a careful limp to a repair shop.

I once came across a multiple fatality accident once when a car lost a front left suspension component. I never found out which but that is what the news articles later reported. This car served head-on into oncoming traffic since a loss of a front wheel or steering component likely means immediate loss of steering control. Do you want to risk lives over some currently modest repair costs? Yes, this is a true story and yes I am trying to scare you into with respect to the potential risks here.

When there is no play in a wheel there are huge lateral forces like Bruce described. When there is substantial play like you are experiencing, the wheel can immediately slam over that half inch and put much greater forces on the related parts, possibly well beyond design limits. Think about a hammer. With it already resting against your finger apply a sudden force.... not so bad. Now raise it a short distance and apply a sudden force. The result is dramatically worse due to the free play and the time that the mass has to develop significant momentum.

If you fix it now it may be much cheaper than waiting to repair the greater damage that may occur when the forces slam over too greatly and shear off some parts and rip your fender and wheel to shreds. Maybe I'm overstating this one? I don't know. But is it really worth gambling with?

Edit: I forgot that it appears you are trying to sell the car. Some of the above doesn't quite apply as to your personal risk, but they do apply to the person that ends up driving it. I sure as heck wouldn't buy it unless the unknown price to repair whatever is causing this becomes a known (or if it was properly fixed as a competent DIY).