I built my own a-frame. I got on pretty thick sheet of plywood, around 3/4" thick, and had the people at home depot cut it into two 6' by 2' pieces.
I got more pieces of wood, most around 12' long, 2" wide, and 1/2 thick, or thicker. Cut them into 4 (6' long pieces) and those pieces should be connected to the ends of the plywood, they are the beginning of the supports.
I got two hinges and just connected the top, and got these screw looking things with a loop at the end, and two 8' long chains basically. The whole thing cost under $100, including the paint, sand, and other stuff we already had.
It is not the best a-frame, but its extremely sturdy, and can adjust to any height my chains will go. If you want my plans, I can send them to you, it would be easier to understand then my attempt at it lol.
I know you can get good quality a-frames all over the place for around $600, so if you keep looking you might be able to find one.
Diane