It will depend on the actual Bo Jackson Baseball Card. There are several different ones and they differ in value.
- 1993 Finest Refractors #91
- 2002 greats of the game through the years level 1 patch
This is sold for $35 online from that same site mentioned above. As you can see the different Bo Jackson cards can be sold for a variety of costs. This one is $40 less than the 1993. It is probably because it is an older card in the above. A 1986 card that is older sells for less than the two already mentioned. It is because it is the rookie card and there are more of them available.
The value of a baseball card is determined by how many are still left in the market. It is also about the quality of the card. A card that is in mint condition will gain more profit than those that were played with. More than that, if there are a lot of the cards still on the market then it means the value is going to go down.
Depending on the cards your husband has you may find there are some worthy of a high value and others that do not. It is best to ask a professional to determine the best values.