You have to pay 3 times. You pay when you send the I-130, then for the medical and finally on the day of the interview. I filed my I-130 back in April so I paid at the old price which was $190 but they have increased significantly. However, I did pay the new price for the medical, though I can't remember how much it was (230 pounds maybe? Plus 60 for shots) . The price for the visa has not changed, it's $385. It's not a cheap processes!
June