Another Aggie forester here. Spent years managing forests on an industrial scale and buying/selling timber. If they were decent to high quality oaks, they could be worth $300 per thousand board feet to maybe $500. It all depends on the quality of the timber, distance to a sawmill, and number of sawmills in a geographic area. The more sawmills, the higher the competition, and the higher the price. The converse is true also.
A fully loaded log truck can hold up to five thousand board feet. So you're looking at $1,500 to $2,500 of stumpage value per log truck.
How many trees on a log truck? Again, depends on size, but if they're big (20" to 30" at breast height... not ground level), think of 10 to 20 per truck as a ballpark range.
Hope this helps.