I'd check and see what he meant by 3 truck loads of fabric.
Then I'd check to see that it was quilting fabric.
Then I'd see how old it was and how well it was taken care of.
Then I'd call all my quilting friends and see if they'd split the cost.
If I couldn't get enough friends, I'd probably pass on the oppertunity. Unless it was absolutely fabulous quilt store quality fabrics with lots of blenders and batiks. That's a lot of money up front. I know that many people probably have that amount or more invested in their stashes but it accumluated over many years.
Definately counter offer and see what he accepts.
Have fun and let us know what you decide to do