The way I see the Mk3 8v is a disposable car. I don't mean it in a cruel way as I drive one myself as a daily driver. I have had no problems whatsoever and have got a full service history with it. It had 92k miles on the clock and its a 1997. Cost me £650. This is why I say displosable because if it goes horrendously wrong or fails miserably at its next MOT its cost me £650 for a car for a year (£54 a month) But on the other hand its been proper reliable and not broken down, only had to change the battery which is fair enough.
The Mk3 8v are cheap because no one wants them

they all want the 16v because its 'quicker' I doubt you would get a half decent focus for 8v money and I think in the longer term will cost you more to run (This is only my opinion based on people I know who have own focus's)