The average person? They'd never finish. I think most people don't read much anymore. I think it would take the average reader a year, using one of those yearly reading plans. This is the way I've always done it. Using the 80 hour benchmark mentioned by farouk, I think it not unreasonable to expect to be able to read it in about 3 months, if you're dedicated.
I think it is important to read the whole Bible, and any Christian who has not done so should do so as soon as they can, however it is also very important that we linger on verses God brings to our attention. Meditate upon them. Pray upon them. So there will be times when we spend many hours on one passage and not make a whole lot of "mileage" in reading a lot of material.