I bet what we have up for our chickens would work! We got wooden fence posts that I think were around $4ish each. approx 4" diameter and 7' tall. Then we got a roll of chicken wire. 5' tall. for a toddler you could have it shorter, course! we borrowed a post hole digger, rammed those posts in there, it takes a little bit of work to pack the dirt in around them to make them good and sturdy and they need to go in about a foot deep. Then, get out a staple gun and go to town! You can use metal t posts as well, but of course then they can't be stapled! There's metal thingies to attach the chicken wire, but we found those difficult (that was our chicken fence version 1) if I were using t posts again, I'd probably just use zip ties. Welded wire is a bit pricier than chicken wire but its sturdier and a bit more attractive. We have the posts approx 10 feet apart, and bought a roll of 150' of the wire and I think it only cost like $60. We got it from a coop farm supply store. Cost less than it would have from home depot, or even our local, more suburban feed stores!
We also made a very effective gate that I'm pleased by how well it works! We used a metal t post, then got some pvc pipe that is big enough to fit over it snugly, but smoothly. Cut 2 pieces of pvc so that it would be a couple inches taller than the t post (the above ground portion of the post!) and 2 pieces that were as wide as we wanted the gate. We got 3 90* pvc joiners, and 1 T shaped joiner. make rectangle out of pvc, and attach chicken wire to it with zip ties. The T joiner is in one corner so that it can slip right over the top of the metal stake. The stake makes it sturdy. We positioned it in the fence so that the opening is next to a wooden post, and close enough so that when closed, it overlaps a few inches with the post so that it can't swing in. On the "hinge" side, we joined it to the rest of the fence with zip ties. We simply place a rock outside the door so the chickens can't push it open, but I'm sure it'd be easy to add some kind of latch. If the description is hard to understand I can take a pic.