Costs of knocking a door through...
 

....an external wall.

I want to do a bit of internal reorganisation. It would involve
knocking through a new front door from an external wall and a new door
through an internal wall.

The external wall is stone-faced breezeblock, and the internal wall is
plaster-covered breezeblock.

For the external wall, I'd like to replace / extend a window to by
french/folding doors 3-doors wide.

Aside from the donkey-work, too much for me, so I was looking for
approximate costs. Typically useless lack of detail I realise, but any
informed opinion would be appreciated.

Thanks

Sean