Roof repair costs

Pumpkinwaffle

Hi all, I know this isn't a simple question to answer but I've just brought a 2 bed semi detached house and the roof requires the following work:

“New roof tiles and felt are needed together with lead flashing against the chimney stacks. The existing tiles could be re-laid. At this time the vegetation on the front and rear chimneys can be removed.

The house is suffering from a significant amount of roof sagging. We are recommending vertical supports are added within the loft space to the roof ridge beam and to the front and rear roof purlins. In order to carry out this work a newer larger loft hatch will have to be installed within the first-floor landing ceiling.”

is anyone able to give some indication of what this will cost? I have got some roofers coming in over the next few weeks but just trying to prepare myself (if possible). I'm based in England if that makes a difference. 
Many thanks 

Slinky

Did they surveyor not give an indication of the costs? Have you spoken to them to ask them?