"到时候费用"怎么理解, 单价? 样品费? 所以只能含糊地翻译如下：
Model No.11 and 21 are still in the stage of internal testing. As soon as the test is done, we will have them submitted immediately for certifying. About the fare you mentioned previously, Model No.18 is the first in kind to be certified by Australia OVEN, so it is a little bit pricey. However, Model No.11 and 21, as its successors, are basically identical to Model No.18, except to power source and some other structures. So the total cost will be definitely less than $500 once being finalized.