When the wood is ready for pickup, you could rent the truck from Home Depot and go directly to the lumber supplier and fetch it to the hacker space ASAP, then return the truck back to Home Depot also ASAP. But it would still add the cost of the hourly rent to the cost of your wood, so might not be worth it. Otherwise, make friends with someone who will either lend you their truck or drive you.
I have had some luck carrying half-sheets of acrylic on the roof of my sedan, however, I have to put a non-skid mat on the roof to prevent scratching,
drive about 30 mph,
use significant bungee cords to lash it down, and
make sure to angle it so that the wind does not get under it and cause it to lift (I use another sheet to reflect the wind up *over* the acrylic sheets). It takes me as long or longer to prep it for the ride as the ride itself, and I'm not sure how it would work with full sheets.