I was in the same boat you were this time last year, trying to find a cheap DIY fire pan. I searched a lot of old posts with suggestions from the cheapest of just cutting off the bottom of an old oil barrel to just biting the bullet and buying the cambridge. Ultimately went with this design - DIY Firepan
Only $50. Some parts were a little hard to find, but everything was available either online or at the local Ace Hardware. It's worked great so far, not too hard to build either. Actually two of my rafting friends were so impressed by the price and design they built their own as well. Only con is it's not legal on the Grand, but hey we all know how often THOSE trips come along haha!