Ok Back again
cheapest convertion would be a single xml in your old housing if it is made from aluminium
approx cost prices
xml on 20 mm star £5
optic or reflector £2 to £10 ish depending on size
driver £10 to £25 ish
switch £5 to £10 ish
heatsink machined to go in your case ??? upto £10 ish
couple of hours work and return postage ???
with the likes of Smudges light £67 I believe at the moment though I think he has some old stock going cheaper .the sensible approach would be get one of those and see (as Rusty mac says ) if you can sell your old battery and charger or just give it away .
and cheaper lights available upgrades dont seem to be as viable as three years ago .
I could do you one of my 4 xpg mini light heads to suit your battery
for about £100