The cheapest build would be to start with a F9 paper model that you can probably download for free. Resize the model to be wraps for standard body tube sizes. As for the fins I personally prefer a removable fin tube similar to Estes space shuttle or Dr zooch flame fins. Now the real challenge here for this model is to find a matchbox , hot wheels style Tesla roadster appropriately scaled, to use as a nose weight. And descending separately would be cool also.