I'm in Thailand and my grill that I purchased a while ago is a standard type charcoal grill. The grill came with a square metal grate that sits at the bottom of the grill and is what you place the charcoal on for cooking. I just found out that it was left out for several months and is now completely rusted through. Much of the grate is just falling apart (see photos). I assume I need something that sits at the bottom and insulates the charcoal from the bottom of the grill... or is it more something for a cleaning convenience? I could still use it and put charcoal on top of what is left of it, but I worry about rust dust getting into the food. I thought about buying a wire grate and maybe a small cookie sheet and putting them together to replace the old grate. Not sure what to do. Any ideas?
You'll want to have a grate at the bottom of the grill.
The grate is what keeps the heat from the charcoal from warping the grill. In some cases, the heat will melt the bottom of the grill and cause the whole thing to collapse.
Plus the space between the grate and the bottom of the grill is needed for good air circulation inside of the grill.
IMO, the best thing to do is clean the rust off of grate with a wire brush. As long as there aren't any large holes in the grate after you finish brushing it, go ahead and cook a batch of hot dogs or burgers on the grill. Then after you've used the grill, inspect the grate. The grate will either be falling apart, or it'll be fine.
If you need to replace the grate, go ahead and do it. If you only need to patch it up, find someone who can spot weld and see if they can fix it.
That charcoal grate was made of "expanded metal", or at least that is what it is called here. Here in the U.S. you can find it in hardware stores, including the big boxes like Home Depot and Lowes. The hardware stores usually only have smaller sized sheets, often only 12 inches wide. Alternatively, any good welding shop should have it available in larger sheets, and often will cut it to size for you. They will also have a wider choice of sizes, meaning the size of the spaces in the sheet, and they may also have stainless steel available, which of course will last longer. I hope this helps.