90 minutes a night! wow.
are you using rechargables already? That would be pretty dim by the end of every shift on alkalines.
If you are using the light outdoors primarily, then I would suggest trying to stick with incandecent.
There are tons of ways to get the runtime you need. You can go with a lower powered lamp in a large "tactical" body (still way smaller and brighter than a 3D mag), or you can go even smaller, (or brighter) and carry spare cells along with you.
When trying to "shrink" the size of the light-source, price goes up. You kinda have to run lithium batteries to get a lot of oomf in a small space...
I'm going to suggest a 2x18650 li-ion configuration. Running a LumensFactory ES-9 bulb. This will give you about double the brightness of a mag3D with a steady discharge curve (stays reasonably bright throughout the discharge) with a maximum runtime of about 150 minutes, this gives you some overhead in the runtime department. Size of this light is going to be aprox 8.5 inches long, 1 inch diameter, (slightly larger at the head and slightly smaller in the body)
The problem with this recommendation, is the price, and the complications involved with piecing it together. You'd have to buy the following:
1. 2 18650 protected cells (I'm thinking AW cells to save on cost here) ~$29
2. 1 good quality charger so you can "set-it-and-forget-it," since you will be charging almost daily. Having to monitor charging on a cheap charger would be a pain. So the Pila IBC charger. ~$50.
3. 1 2x18650 body (leefbody) ~$70
4. tailcap/switch ~$40 for a surefire/leef type switch
5. bezel, ~$15-30 depending on source, G&P makes a cheap one that would work fine.
6. Lamp. should probably buy a spare also... so about ~$30 total for 2 lamps shipped.
notice how we're up around $250 for a compact rechargable flashlight. bummer eh?
ok... so lets cut some corners and make it happen...
1. 2 Brinkman maxfire LXs $17 each at target. 5.5 inches x 1 inch. tiny. (this way you have a backup ready to go, extra runtime on board pre-loaded)
2. Ultrafire WF-139 charger. You need to monitor this one and remove cells when it goes "green." But it's cheaper, only like $15 online.
3. 2 protected 17670 cells from AW: $24.50, more if you want more spares, each cell fully charged will provide about 50 minutes runtime with a ...
4. LumensFactory HO-4 lamp (x2, one for each flashlight) ~$30 shipped. This is a little brighter than a 3D mag. with a much nicer beam, soft focused center spot, no artifacts in beam.
total $103 for 2 rechargable flashlights.
there are endless options like this...
LED61s idea is great, but I think I would suggest stepping down to a lower powered lamp with your runtime needs in mind. The EO-9 is a scorcher but will only run about 40 minutes on those cells, so either more spare cells or lower powered lamp. (the ES-9 would run about 100 minutes on those cells)
You can also piece together something cheaper from more common flashlights... Like... for example... find a 2AA flashlight that takes PR based bulbs, that you like the look and feel of and think would be tough enough, and drop in a 6 cell mag xenon bulb and run it on a pair of 14500 li-ion cells. Bright as a 6D mag in a 2AA formfactor with about 40 minutes runtime per set of cells.