unfortunatly the ingrediants can end up costly,i got lucky with mine and found a new old stock genuine rod kit for a bargain,and a piston kit and mains cost what they cost.
the biggest shocker will be gearbox parts,usualy 3rd and 5th gear pitted badly,mine needed 4th gear drive also so ended up 300 quid of gearbox parts almost.
i think you could realisticaly end up 600 quid on parts on an early xt/tenere motor without too much trouble.
i chucked a rod kit and piston in my 34l tenere,left gearbox as was,done 4000 miles around europe on it,without a problem and am now giving it a little birthday now and doing gearbox now ive sort of bonded with the bike a bit.
ive now realised its quite a versatile bike,huge tank range,better off road than most of the newer wannabes as its 40kg lighter.
ive had a new model 660 tenere previously and im sort of thinking the original one was realy quite a bike in its day,im thinking theres not much you can buy now that will do same without spending fortunes on bigger fuel tank?