One free or inexpensive method is to use your existing hardware such as your notebook to act as a virtual WiFi router. There are a number of Free or Open Source utilities available, such as
Virtual Router,
mHotspot , or
Winhotspot. These will allow you to share one net connection with all your devices. Even from another WiFi connection. They're basically just front-ends for Windows hosted networks, but saves you from having to deal with the command line.
If this fits your needs, than it can be done for free. However, your notebook's built-in WiFi adapter may not have the range using campground's WiFi. So you may have to invest in a long range external USB WiFi adapter such as those made by Alfa. These can generally be found for less than $25. Just don't be swayed into claims that these are 1,000/2,000mW power. The best will peak around 600mW, still about ten+ times the power of built-in notebook adapters.
If you have a mobile data WiFi hotspot, than don't need a separate router. Most can easily handle 5-8 devices connected simultaneously.
