Does my Peugeot need another diagnostic? ABS issues, help please!

[Lovemycar19]

Hi. Im hoping you can help me! My car displayed problems with its abs a little while ago by the abs light coming on the dashboard. I had a diagnostic run by a mobile mechanic. He said the fault was coming from the back abs sensors and that they may need cleaning or replacing. I had the sensors cleaned and this didn't work so I decided to book in for the sensors to be replaced. But driving the other day, my dashboard flashed up with the STOP sign and this didn't disappear up until getting the car home 15mins away.My friend in the car noticed it flashed up with 'breaking fault'. So I took the car to a different mechanics, (a short drive about 5mins) and the stop sign didn't appear in this time. They checked the car and said they didn't think it was the abs sensors but the abs pump and maybe the computer. They said it would need to go to a Peugeot specialist. I now have the car booked in for a diagnostic with Peugeot who are charging me £53 per half an hour and that they don't know how long it will take to find the fault. Do I need to run another diagnostic or can they tell from the other info where to look? It's starting to cost more and more money. My mother had this problem with her ford with the abs light coming up - she was charged so much money to then find that all she needed was new fuses costing £2. Please help! Many thanks!