Martin,
Lee has the cheepest dies at around 75 USD. The expensive part is that you need a special press as the dies are quite a bit bigger than the standard 7/8 - 14 threads everyone else uses. Lee sells a larger press which costs a LOT less than the next best one.
Once you bought the bigger press, you would be all set to reload 50 Browning Machine Gun, though!
As soon as the permits cleared.
The bullet mold is also more expensive than most. Then consider the large measure of black powder needed to fill the case so that no air space remains under the bullet. The bullet sizer would not be too expensive ( compared to the other items needed) Your friend could slug his bore and order a custom sizer from Lee for 25 USD + shipping. No top punch would be necessary as that system pushes the lubricated bullet
upward through the sizing die.
www.Buffaloarms.com www.grafs.com www.midwayusa.com are 3 places to get reloading supplies for the Martini-Henry.
I had a "Peshawar custom" Martini-Henry artillery carbine copy and meant to shoot it but gave up on the idea after researching the cost.
Our pal Bruce has it now!
SW