Lick
(Lick)
10
If you don't mind modding, the S2 on sale at gearbest is usually the cheapest, but I would swap the LED and the driver. I would get an LED from here: http://www.kaidomain.com and probably get the BLF driver https://www.banggood.com/Astrolux-S1-BLF-A6-A17DD-L-FET-1-2_8-4_35v-7-4-Modes-Flashlight-Driver-p-1009980.html
The driver can be flashed if you want to go that route too. I don't know too much about that yet.
But really I think its best to get an A6 and go from there. ;)
If you want to go even cheaper, get an SK98 from eBay. They will all suck. You will not want to keep the body either I don't think. But you can try there if you want.