What is the cheapest way to build a fence?

Obtain some free pallets long enough to make the fence the height you want.

You could put in the 3X3 or 4X4 posts every 8 feet and then add lattice to the whole area. Dig a hole for the posts about 18-24 inches deep put in your post and then pour in the concrete mix. It will solidify and hold the posts. Be sure to get a post leveller so that your posts are standing level and straight before they set.

Free pallets (In my area, not free), lattice panels. Or look on nextdoor.com, Craig's list or freecycle.org. see what you come up with.

what is it for? how strong? Privacy? that's what will determine what to use and how well it needs secured. are you in city need permit to install cement posts build fence?Have any code enforcement(city,HOA?)on type of fencing allowed? Cheapest /strongest way--Put in/sink metal fence posts around area and get rolls of goat wire,livestock wire or chicken wire --along with baling wire for attaching to posts.This fencing comes in different heights and lengths of rolls.The difference in the space of openings will matter if you have smaller animals to keep in(chicken wire small openings over entire fence-goat wire smaller at bottom increasing to larger as you go up fence-livestock larger openings thru out entire fence good for big dogs/animals. Need more private add bamboo rolled fencing to wire fencing to block views or even lower cost option add landscape fabric along fencing. Next lowest cost use pallets if you can get them either just use whole pallet as panels or use wood from them,need good strong posts and cement installed to hold weight of them. if you are just fencing in small garden area use rebar as posts and attach chicken wire to it with either zip ties or baling wire. you can buy rolls of wood pickets and wire fencing to put up using either rebar or heavier duty metal fence posts just depends on height of fencing and purpose. need to know some answers before I can really tell you best option for your use

The cheapest way is to get your neighbor really mad at you, but that is not usually a good idea. Try Freecycle. There are some cool ideas using old doors on Hometalk. If you have access to fallen trees or branches you can weave a fence. Problem is too, that cheap may not last long and you will be looking at more work down the line.

WhaT is it for? To keep something in/or out? Safety? Children? You can get vinyl deer fencing with 2; square openings, 4” openings? Zip tie it to trees. This stuff is STRONG.220# strong. Black so it disappears out of view in the distance, can be 7’ tall and less. I used it around a garden. Got 14” legnth zip ties. Google dear fence. I got 100’ for $100. Where i want privacy? I planted morning glories...beautiful!