Takes ages to start

Hiya...

I've got a 1996 Audi A4 Avant 1.9 TDi. This morning it took ages and ages to start, even thought the little glow plug light came on and went off again.

I'm guessing that maybe the glow plugs aren't getting any current as the car does start if I crank it for about 20 seconds. It does sound horrible, but hey, I need to get the car to go.

My questions are these... A) If I can't get to the garage to get the glow plugs replaced until Friday, am i going to do any damage to the car by cranking it until it starts? B) Could I buy glow plugs and change them myself (being a girl i'll give anything a go once, but if it's too complicated i'll get the professionals to do it and C) If i get a garage to do it, how much roughly should it cost?

Cheers!

Donna x