A pair of steel rails from an old bed came in handy to make a pair of forks for my small tractor. Besides the rails, I used two inexpensive load binders (these are less than $15 each) and some chain. Total cost should be under $50. Regular angle iron will be fine as a substitute for the bed rails but you will need to modify the way you attach the chains at the back of the bucket. Matter of fact you might even elect to buy regular angle iron just to have a heavier lifting capacity. I haven't checked the maximum load capacity of my forks yet but I know that together they are good for 300 plus pounds (see video).
So far I have used the forks to move garden furniture, relocate some old trees and branches, move about some heavy hardwood pallets (I use them to make raised bed gardens), move a large garbage container, carry my compressor about to help me with some fence repairs, and a couple of other things. It is pretty easy to change the spacing of the forks to match the load (see video of the compressor being loaded).
You will need:
2 load binders (Such as Harbor Freight #36638 $12.99)
Approximately 15 feet 1/4 inch chain
bed rails or other angle iron (I cut mine to 58 inches but will likely make them shorter by 12 inches or so). The rails shown in the video are made from 1/8 inch steel and are about 1-1/4 x 1-1/4 inches
2 rare earth magnets
2 quick link chain links (or suitable alternative). Note: If you use regular angle iron you will like need four of these links as the back end of the angle will need a different attachment method than the one shown in the video.
All sizes and dimensions will change (likely go up) depending on the bucket size and the desired load capacity of the forks.
My tractor is a Kubota BX25 compact tractor. This fork design should be ok for other tractor sizes.