100ll is free if you know the right people. Bulk plants that maintain Remote fuel dumps must rotate their stock every two years and recycle any partial or over age barrels. Once the seal is broken pilots will never pull fuel from that barrel again for fear of water contamination.
The fuel is recycled as if it was used oil so if you happen to know someone in a bulk plant who handles it, you can likely get it free, just bring back the barrel.
I used to get a barrel or two every winter for sledding, but when the bulk plant finally shut down, I got 7 full barrels including 3 with seals intact. I processed everything through a water seperator and ended up with 5 full drums of perfect fuel. Mixed 50/50 with Regular it ran all my toys for 3 years.