A fallow doe with a larder weight of 36kg (guts out, head & legs off, skin on) will yield about 20kg of saleable meat (all boned out).
For budgeting purposes, you can roughly assume that the larder weight in kg, multiplied by 10, will give you the approximate retail value in £s of the butchered carcass.
(So a 36kg larder weight doe retails at around £360).
That formula seems to work fairly accurately with fallow and reds. Not tried it with other species.
(Obviously the return on the carcass goes up if you do further processing, such as burgers, sausages etc).