I have a MK1 diesel estate, pre-TDCI. Economy is about 42-48mpg. I suspect slightly worse than a MK2. Still, the money you save will easily pay for the negligible diference in mpg difference. And, if anything goes wrong which it may or may not you have a larger pot than if you go for newer. Also, there will be less depreciation the less you spend.

If you end up going for a MK1 it will be more fun to drive of the two. Just make sure you check rear wheel arches for rust. Hope this helps.

BTW, cambelts are cheapish on my MK1 pre-TDCI, only needing changing every 100,000 miles. When I bought mine I didn't know when it had been last changed so had it done as a precaution.

In 2001 I drove a rental Mk1 Focus estate TDDi which I thought was surprisingly good. In 2002 I drove a rental Mk1 Focus estate TDCi which I though was even better.

Both drove with verve and with the ability to go many miles each day without discomfort. If you can find a good example, go for it.