I tried the route of making cheaper flat faced rims, about 8 months ago. But I couldn't get the perfromance I needed out of them. I bent a few of them wthin the first few weeks, just by jumping high and landing crooked. My 7 year old is a speed freak, and likes to slam into things at full speed.
Since I've had the Iron Cross on for about 5 months, they still run true and straight. I've seen movies of guys jumping the Vipers off houses, with no damage.
As far as the lowest cost, go for the Iron Cross or Rattler, they are the least expensive. Most of the distributors are selling my rims about 10% off my website price. Or, you can pm me and get 10% off the price as well.