I would not recommend milk crates. I come from the dairy industry and most dairies try to get milk crates out of their facilities for good reason. They are actually quite difficult to clean effectively with all the niches.
Obviously, they are great utilitarian devices for a variety of applications, but they absolutely suck in terms of sanitary design and cleanliness. Most auditors would not like to see these being used except for their explicit purpose of temporary milk storage.
Plastic pallets would be the better alternative as you can get designs that are easy to clean. Additionally, you can get them in a variety of sizes. If this doesn't work, depending on your budget, you can get stands made/fabricated out of stainless bar. It would basically be a small square with legs.
Thinking outside the box...if you want a cheaper alternative you can simply get designated colored buckets that you can invert for the sole purpose of keeping your weighing buckets off the ground. Of course, these will need to be a cleaning program and require handling protocol. A very cheap option...then again, it is a cheap option which the buckets likely won't last that long.