To understand what the problem is you need to put a code reader on the car. You will need a Freelander specific reader. As you may not buy the car - its probably not worth buying a reader - better to take it along to a garage that can read the codes - I seam to recall someone saying Halfords do this in the UK?
Its only when you know what's wrong, that you'll be able to determine how much it will cost.
You say you've been 'offered' this Freelander - does that mean you know its history? If its a goodun, it may be worth taking a hit on fixing the ABS, you never know what you might end up with if you let it go!