Ask them if they can break it up into payments for you.
Also, they should have let you know there will be a fee if the trouble was on yourside of the Network Interface Device.
Thats why they tell you to go to the NID and plug a working phone in to see if the trouble is outside the premise or inside.
If this wasnt explained to you, then work that angle.
If it was and you just didn't feel like doing it, then why should they send a tech out?