The Aluminum Box Mystery

I am trying to buy a 1996 Cadillac SLS with a 3.2 Northstar from an associate. I have seen it, an besides a few dings, it looks pretty good. When he tried to start it up, the engine compartment made a clicking noise. My associate, who says he knows a little about auto repair, says that it needed a new battery. Smoke was also seen coming from under the hood on the opposite of the battery side. I gave him a few bucks to buy a new battery and while he did get it to turn over, he said that the smoke was coming from what looked like an aluminum box with wires leading to it or away from it. I have to say, that I really don't trust this guy or his opinion, but I am in desperate need of a car and the owner only wants $750 plus whatever it cost to get it repaired. A friend of mine, who knows something about cars said that it sounds like the onboard computer which can be pricey. I'm willing to pay for that, but I want to make sure that it doesn't sound like a $2,000 problem, like the computer wires leading to something else screwing up something else. The motor was rebuilt a bit ago and the trans was said to be fine. I desperately need advice from anyone who might know what is the problem and how much would the potential damage be, price -wise?