We don't know how far it is to the nearest available internet connection. Assuming the nearest internet connection is at the house in which you live and the barn is within a couple hundred feet of the house, then it may be relatively affordable. If the house is on one side of the 100 acres and the barn is at the opposite end of the 100 acres, then it will cost a little more. We also don't know if the barn has available power and how reliable that power is.
1) House and barn are within a hundred feet of each other. Install a wifi access point outside the house. If it is not rated for outdoor use, it (and the cabling for power and Ethernet) will need suitable protection from the elements. The access point needs to be line of site to the barn. This could be as easy as mounting the access point to the side of the house, under an eave or as complex as running appropriate cabling, setting a post in concrete and mounting the access point at the top of the post (a 12 foot 4x4 will do). Lightning protection will likely be needed. Power will be needed for the security camera system. This could be a CCTV system with an NVR (I use Swann, Fostex, Sony, Samsung and a few others are fine.
A variation on this is to not use wifi, but trench for conduit and run the cabling from the home to the barn. The Swann camera on my system are CAT6 (or CAT5e). Power, video and audio run on that cable so there is no separate power for the camera or the NVR. The cameras are installed at the barn, the NVR is in the home. Ethernet has a limitation of 300 feet, so design accordingly. The distance is from the NVR to the camera, not from the house to one side of the barn.
2) House and barn are more than a couple of hundred feet apart - but less than about 500 feet and the barn has power. You'll need to do the first wifi option (above) - and at the barn (side facing the access point) add a network extender. The extender plugs into the NVR, the cameras connect to the NVR. The NVR plugs into the network extender and connects using wifi to the access point. If the barn has no power, then we need some sort of generator to provide power to the network extender, NVR (and the cameras). A solar generator with an 100 app-hour battery should be enough for overnight + a few cloudy days. I've made a couple of solar generators for about $1,000 each. In your case (barn), it might be best to install the inverter, battery and solar controller into a metal cabinet to minimize fire potential. There are several videos on YouTube that are really informative.
3) The house and barn are not close to each other. In this case it might be easiest to use a satellited internet provider just for the barn. Like Hughesnet (this is not an inexpensive option). Assuming line-of site, a medium or long range directional wifi bridge/extender may be needed - suggest hiring someone who knows what they are doing...
There may be some other options/permutations, but my point was that we did not have enough information based on the information you provided.