Hi Ya,
Don't know that much about the Astra's apart from there is supposed to be problems with the intercooler on higher milage cars so you might want to look at something else or a non turbo if you can do with a very slow car.
As for the golf you will find very little in the price range. (soory have just bought a HDI my self and was looking at golfs but nothing for less than £3500 that was any good and had FSH)
You might want to look at the 306 TD as the engines are great. I have 2 the first was write off (some running into me at speed) with 170,000 and did not cost a been to run and the last one which I parked in the back of a golf at a very funny angle had 260,000 on the clock and was as good as ever, all I had done was a heater matrix at £300 and full service only costs around £80. GREAT CAR AND ENGINE
You should be able to pick up and R / S reg with under 100,000 on for the money your looking at with FSH as well.
Hope this is of help.