rave, i'm going to have to pick at that a bit. while, on the whole, you are right, your payment examples are not quite true. lets say you've got 100k mortgauge, at 5% interest, over 25 years. for sake of ease, lets say you're paying off 1/25th of the amount, and all the interest every year (doesnt work like that, as that'd mean less in latter years). in the first year, the cost would be £9000 (5% of 100k + 4% (1/25th) of 100k). if interest rates went up to 6%, you'd pay an extra £1000, but that's only an extra 1/10th of the total cost. still a hump, but not a killer.. secondly - you say you'll move when renting becomes more expensive than buying - not sure if this'll ever be the case - the reason why buying is cheaper is because at the end of your 25 year stint (yeah, a long way off) you end up with an asset worth more than anything else you own, and you'll never have to pay rent again..
back to OP, you say you want lowest repayments possible - is this really the issue for you? for me, i comfortably earn enough to pay back £1000/month (if i wasnt paying rent), but, no-one will lend me more than 5x my income, which basically would work out at around £800 per month. and that's before i rent the 2nd room out, or whatever. either way, its not enough money for a decent 2-bed place round here, so i'm stuck for now :|
getting into the housing market is always a gamble, whatever it is doing at present, for the next year it could either go up, or go down. its slowed this year, but could still go either way. i'm hoping it'll crash, but i realistically don't think it will so i'm saving lots towards a deposit in the mean time.