Expensive is a relative term. It should be easy to see if the alternator is the problem. Slip the belt off and see if the engine turns over. If it does, run a compression check. If that's good there's only a few other things. It could be the relay that switches the fuel pump from battery power at start to alternator power when running (you want your fuel pump to stop pumping gas when you crash your ride). Or (as in my '89 p'up) the fuel pump lost power from corroded wires or the engine ground is no good, but it reads more like an alternator issue. The light's going to come on and the power steering will get sluggish 'cause the engine stopped so it's hard to say. For $400 you can barely buy a set of tires much less a vehicle to set them on. The fuel pump is pricey but I've read more posts about corroded wires that truly failed pumps.