I've got about 20k cards that belonged to by brother before he passed. Just something I've held on to, but never played.
I am going to apologize in advance for the insensitive statement I am about to make, as I am sorry for your loss and sure they are worth more than mere money to you, but...
Magic cards, especially ones from the 90's, can be worth anywhere from $.50 to $50 a piece, on average. Some, like the basic lands sell for less, and a few sell for waay more, but you are potentially sitting on a new car's worth of money there.....