I don't think in the long run much is wasted. And what is, is a trade off for how quickly the pig cooks.
Ash doesn't fall on the pig, unless you screw up, or have really hight winds. You remove the coal pan, and rest it on the long handles when going after the pig.
Downside is, unless you use some sort of smoke generator, you won't get much smoke on the pig. Cinder block pit would be cheaper, but bigger and bulkier. You can definitely cook a lot of food at once.
Smoke-In-Da-Eye here on the forum has posted at least one pig roast worth of photos