@heavanet- If you have to replace a microwave part, the turntable plate is the easiest and most affordable part. However, you can't just use any type of plate, because you need one that has the groves to fit your particular microwave model. The plate also has to be made of the special glass that is strong enough to withstand daily microwaving.
If you have a kitchen specialty shop in your area, this is the most convenient place to look for this type of microwave replacement part. These stores often carry a variety of repair parts, especially one that is as easy to replace as a microwave plate. Some retail stores also carry microwave plates, but you are probably less likely to find a plate that will fit your model in that type of store.
If you can't find a plate to fit your microwave, you will probably have to call the manufacturer. When you do, you will be able to provide the model number for your particular model, and should be able to order a new turntable plate for it. Though it might be a bit more costly than one you find in a store, you will have the peace of mind of knowing it will fit and will be a high-quality part.