Fastest, and definitely the cheapest is setting up a Par 3 (I do 9 holes) in your CC. I set them from red tees, low wind, tourney greens. I get 10-11 rounds per ball (level 34 cally) and it takes 8-9 minutes per round (Avg about 220 XP per round). Just 6 rounds in an hour will get you 1300+ XP's. Using a boost will get more, of course. I hammer away at them, and it's quick, easy, and cheap.
To show how cheap it is, when my ball hit the red (25% life left, I think), I played 3 rounds and still had a few hits left. My CC owner allows me to set a different one every 3 days. The really god thing to do would be to not play one day, the play a round and wait until a couple of minutes before next day begins (&pm EST where I am) and buy the 40% boost for 1 hour, then play that last shot, get the CDP'd XP's, and then do another quick round (preferrable Par 3 tourney, not practice), and get those CDP XP's and play bonus times 40% again. Plus, you'll still have time for 4-5 more rounds at 220 x 40% before the boost runs out. It would add up.
I don't buy the boosts (over-priced to me). I even play many times with a starter ball just to knock out the quick XP's.
There is no other cheaper, faster way. I've tried the 9 and 18 hole toutes, and the 9 win hands down.
Look at my score history.....Par 3's all over it...and I'm off to hit a bunch more right now. I need 18,000 to get to level 97, needed 100,000 2 weeks ago :-)