I realize it may be a regional thing, as I've read that some Walmart's and Deli's/bakeries don't give the buckets to customers, but around here it's relatively easy to find free 5 gallon buckets with lids.
I stop by my local WM or a regional supermarket w/ deli around 8 am on a Wed. or Thurs. morning when driving home from work. I generally manage to pick up 8-10 buckets per month, and have for a couple of years now. That's all I realistically need, and other folks seem to ask for them as well.
The "
hanging tomato from a bucket" craze last year really stepped up a demand for them.

A prepper buddy of mine ordered his from a plastics company (sorry, but I can't recall the name of the company at the moment), along with a bunch of Gamma Seal lids. He has a cash flow that allows it, and limited time.
If you have the time and inclination,
and live near a Walmart or supermarket with a deli...it could save you some funds. It makes a difference for our household and frees up funds for additional prep items.
Good Luck.
Prag