@Marine this question is kinda stupid to ask because the prices can really vary. Some ppl might get lucky and get a specific skin for less than a dollar, but some might end up spending more then $100 for the same skin.
Also, there are some skins that were only available once only and will most likely never return ever such as bape suit, some old og gun skins, popularity, etc…
it makes it impossible to estimate a total cost or an approximate either…