To date mine is a Sipik sk68 MC-E colour-mod I did last year: host was $6,67 , led+board was $19 , so the parts/host ratio is 19/6.67= 2.84 The parts were 2.8 times as expensive as the host.
(not added: work+love that went into it ;-) )
Very good question djozz but unfortunately I cant go there. Say a light costs $25.00 such as the Defiant 3C. Driver upwards of $20.00, lens $6.00, copper and aluminium $35.00, plastic for switch and switch $10.00, MTG-2 led $22.00, batteries $30.00, Labour, power and misc stuff forget about it and it goes on and stuff you break or blow up again an unknown cost. Forgot. $30.00 postage just to get that original $25.00 light to Australia. I have three so theres nearly $100.00 in postage costs.
I have a shelf fool of lights like that and then there’s the ones you give away.
I must stop. I think I have just talked myself into resigning from this money spending whatever we call it. No I’m not rich, far from it like 99% of other people here.
djozz. Maybe the title should be changed to how many fools spend all there money modifying perfectly good lights?
Mine was probably pretty minor compared to others. I bought some cheap UF S5s from Ebay ($2.99 + $1.00 shipping), and then went nuts with triples.
MCPCB - $0.50 - IS
Carclo - $$? - IS
3 x XP-G2 - ~$19 (Digikey)
Solder paste - $15 (Ebay)
Driver - 3.04A - ~$6 - IS
7135s - ~$2.00 - FT
Pain of stacking - ?
You can add it up and compare to the $3.99 for the S5 host :)…
MXDL 2xAAA Penlight as host: 3$ (love it!)
Nichia 119 + Ledil TIR + Parts for high-eff buck driver: 15$ (Wow, thinking about that makes it feel somewhat wrong :P)
Makes a ratio of 5:1.
Self-deception helps thought. I keep my electronics and flashlight hobby seperated in my mind and split the costs.
It’s even somewhat educational, so I can’t really be mad at myself for spending money without a need, right? …. right?
Seriously, I am quite happy I still get a kick out of small inexpensive lights. 
Oh no, i did not mean to make you contemplate about the ratio of the hobby, please stop thinking now and go back to your lathe! (And I specifically requested not to add labour and madness to the costs!)
We can’t avoid the labor nor the madness, unfortunately :)…
$20 for 6ft of aluminium tubing, enough to make say 10 lights. Each light with $10-40 driver, $10-40 batteries, $10-20 LEDs. Nah, the housing is the thing I think of least in financial terms and the most I think of in fabrication terms
Usually, the host is about 1/3 to 1/4 of the cost, but it fluctuates greatly depending on the build. A Solitaire host is $5. The components bring all of it up to about $15+. The EA4 Caveman was about the most expensive host I've ever done and it was about twice the cost of the components to mod it.
A mod with a MT-G2 or SST-90, with a Taskled driver makes the component cost so high, it's just not worth doing a mod and usually a host for that would be about 1/2 to 2/3 the cost of the components, just because it's usually a much larger light that is used for the mod.
Torchlab triple drop-in: $160
Solarforce L2m host: $13
Ratio would be 12.3:1
Hmm, that is a tough number to beat. (but I may take up the challenge 
)
Solarforce L2P gold host, $24 Mclicky switch ~$6, Triple Nichia 219 with custom firmware $150.
Maglight $15, Jayrob modification and heatsink, $160
Maglight $15 Elektrolumens puck $80, 3 Imedion “D” NiMH $60 , Maha charger to charge those massive cells, $65
I too am beginning to wonder where the budget is in a budget light….