There are numerous lodging options in the greater Eau Claire, Altoona, Chippewa Falls and Menomonie area. Use your favorite internet search engine and search for:
Note: FREE rough camping/no utilities, available at Chippewa Valley Expo Center July 5-8, 2018 on a first-come, first-serve basis
You should be able to find something to your liking. There are 3 sites very close to the Chippewa Valley Expo Center and many others within a 30 minute or less drive. The Expo center is on the northwest side of Eau Claire and close to the I-94 and US Hwy 12 interchange.
This a great time to explore northwest Wisconsin, either before you come to the Train Expo or afterwards, or both! There are lots of lakes and streams to fish in, city, county and state parks for you to visit, historical and railroad museums, trains to ride, and fun things to see and do in small towns, bigger communities and out in the country. If shopping is your thing there are great places for that and of course the ony Train Shop in west Wisconsin is in Eau Claire.
The map below shows the area around Eau Claire and the Chippewa Valley Expo Center. Each red dot identifies one or more lodging sites. In Eau Claire there are areas with multiple hotels in close proximity to each other. So there are more places than red dots. A search as mentioned above will help you to identify individual places.