wrtiii is spot on. I've been in business for over 12 years and I've found buying even a few hundred feet won't be worth it. If you want to make 1,000+ tubes then it might be worth it, but I doubt it. To get good pricing on HDPE pipe you need to buy 10,000+ feet. Many companies won't even sell to an individual.
How many feet are you looking for? Here are some additional thoughts:
Do you have the equipment to make the plugs?
Do you have a trailer and the time to drive to get the pipe or do you want it delivered?
Don't forget all the time it will take to get this setup, which will take hours.
What about the tax and all the jigs, wood, staples, gas, time and money?
I am confident.... if you pay yourself $20.00 per hour, by the time you spent trying to find the pipe, get the pipe, pay tax, gas money, buy all the equipment, staples,wood, etc. you are going to end up paying about $3.00 to $5.00 per tube.
People have told me "never again" meaning they have done this before and they said they won't do it again. It's too much work, time and money.
Not trying to steer you away from doing this. Knock yourself if this your thing, but trying to give you something to think about. Most of my customers don't want to mess with because of what I just said. They want to focus on their show.