Hello, I hope the following assists you.
Firstly the labour cost and parts will vary depending on where you have the work carried out and where the parts are obtained from, a main dealer will have a higher hourly rate than an independent garage and genuine Citroen parts will cost more than pattern parts.
The official labour time for removing and refitting the cylinder head is 13.1 hours, the labour time for replacing the DPF is 0.8 hours so you have a total of 14 hours labour.
Parts would be around £80 for a head gasket set including new bolts, a timing belt kit can be bought for around £70 upwards depending on manufacturer and a DPF is available from £130 upwards again depending on manufacturer.
I hope this helps, as I said earlier this depends on where the work is done and where the parts are sourced, the main thing is to make sure you don't pay more than the official Citroen labour times given above.
Let me know if I can advise further and I'll reply as soon as I'm able to.