Fitting new gearbox to 1996 v81 disco1

Can any one tell me please how hard this is to do?
I,ve been offered a recon box at a great price from a friend as mine clunks when going into reverse and sometimes through the gears.
I would like to get an idea of how long this would take a garage to do and a rough costing. I would also want to change the clutch as my landy has done 130,000 miles.
Also do you suggest any other changes whilst doing the gearbox swop?
Thank you in advance
Tayfix

just having mine done at the mo

got a brand new clutch kit for £70
2nd hand gearbox and transfer box for £150
and fitting is £200

Thank you for the reply, is that fitting at a garage? And do you know how many hours labour it takes to do the change over?

yes at a local garage

garage with proper kit should be about 6 hours (so a day probably allowed)
did my fender on the roadside (at home) in 10

Thanks guys