Replying to building rails

i'm gonna throw together some beginner rails over the next week for me and a few friends. i'm thinking a 20' flat bar, a flat-down and a up-flat-down. I'm gonna buy about 50' of 3' x 1' rectangular steel tube and weld them to posts we anchor in the ground. we'll be using those little foundation tubes to make the rails solid. i'll spend no more than $150 hopefully.

i'm just looking for a lil feedback or any other ideas before i sink the money into this.