Baby gate made from a pallet. Total cost $15-$20 depending on the hinges and handle that you pick. I did put a clear coat on it after I was done sanding it. I chose a handle that is for screen doors and so it can lock from the inside. The best part is that my 5 year old can work it, I don't have to get up to open it each time for him. Here is the link to my step by step tutorial. http://davidandallisonhardy.blogspot.com/2015/01/diy-baby-gate-from-pallet-materials.html
Check out this project on RYOBI Nation - Needed a baby gate for the top of our basement stairs. I took out the existing basement door, and placed a by wooden baby gate. Made from common boards, sanded it down, stained it Golden Oak, screwed it
Instead of doing complex criss cross wood design, just do plain planks, stain light sandy colour and pain on a beach scene or incorporate a printed pic. Give to mom as doggie door (for keep dogs off stairs).