Why fence at all? I bought a drag for a couple hundred, and a harrow for a couple hundred... use my pickup to harrow the "arena" then the drag to smooth it. I have a 100 by 200 smooth area to work my horses and the grass/weeds grow around it... clearly defining the area. I put my other horse in a stall or the front paddock while I use my arena, which is right behind my barn on my five acre property... it works well for me, maybe something for you to consider. A 20 foot wide arena is REALLY tight.
There is no passion to be found playing small - in settling for a life that is less than the one you are capable of living. - Nelson Mandela