Harnesses are pricey, but plugging in something that is ready to go is nice. Beats potentially frying something. I got lucky and found a new PnP harness doe my S2000 for $150 on ebay. I'll be going from an AEM v2 to an Elite 1500 on that car.
We are currently making a full harness for a 2500 on the old SHO's right now... It'll probably be a $1500 harness, but it will replace the OEM harness completely.