Do you have farmer connections? We are farmers and my dh took a cleaned but used 2 gallon bucket to the chemical supply place. They filled it for him and said "thanks for doing business with us".
And seriously, the amount they gave me was probably floor sweepings to them.
My dh pays pennies per TON for urea. Even if I did pay for it... whoa... cheap!!!
A farm chemical supply place. You may have to pay for it. They may not want to deal with a small user. But you can call and ask. Plus no shipping charge! (Urea is a great source of nitrogen/fertilizer for a farmer to apply as it is topical and the ground isn't worked to supply it. We are minimal-till to no-till farmers to save the soil and the help stop erosion.)