I'm not sure what city this is located in, but you could buy the property at the tax sale. Are you certain nobody has purchased the taxes already?
If not, then you could buy the property for the taxes owed. I'm not really familiar with tax sales in MO, but I think the redemption period is three years. You earn interest of 10% or 8% depending on when you buy it, I believe.
Or you could take a different approach with the son. Let's say you are prepared to pay up to $20K for the property. That leaves about $10K the son would receive at close. Offer to make a contribution of $5000 to Wounded Warriors or a charity of his choice and do so in his name.
Or maybe he has some children who could use (or have) an education fund. You could make the proceed check out to that fund.
What's important is to let the son know that he won't be required to deal with the sale... you'll take care of all the details and make it easy on him.
One last piece of advice. Get an attorney involved with this sale. Because there is a death involved, and it doesn't appear there was court action, you don't want the sale to be nullified years down the road by some other heirs. Make sure your attorney agrees everything looks correct before proceeding.
BTW, if it is in St Louis county, didn't they just hold their tax sale last Monday?