Plastic tanks are fairly cheap. You could add a 200 gal tank easily. For around $279. Then you have a skid sprayer, (if you added a reel and hose).
What kind of pump? How much is the output? Gal per minute? 2 gallons?
Will it spray 50 pounds pressure? 100 pounds? How high would it reach if spraying trees?
http://www.usplastic.com/catalog/def...arentcatid=838