Thanks)!
I’d go for the Convoy S2+ with 6 chips, tint 4C (for the 18650 type battery) and as stated above, Sofirn SP10B for the AA/14500 (LiIon) variant.
Ladda AA NiMH accus from Ikea are good. Also, 14500 type Lithiunm made by Soshine - 900 mAh, the button top white/yellow variant.
The BLF A6 non-annodized is also available from Ali, but is a little over your $20 budget. See this You Tube video for a review. The BLF A6 is a classic (and my personal favorite) in the 18650 tube-form-factor. If you don't get it now, perhaps someday you will. Take care, and welcome to BLF!
Thanks all!!
And one more question is there any difference between that s2+ in gray and black color besides the color , because as Ive seen gray has been ordered much more than the black one ?
Well, there’s gray-gray, blue-gray, and black-gray.
The UV version comes in the black-gray, the “gray” is typically the blue-gray, and I forget which is the one you gotta order to get the gray-gray.
Not sure if still active, but bilakos had a coupon code not long ago for Astrolux S1 which is the same as BLF A6, shorty version for $16:
An 18650 tube is about $3.
The vendor for this A6 deal was (is) BangGood, and I don't think they ship to Serbia. During my trial checkout, Serbia wasn't a selection in the country dropdown. Skovacijer, have you looked at BangGood.com?
Sooo, where do we get these?
Blf A6 is a good choice .Only downside is the tints are kinda sucky .
The grey S2+ is the old one with sharper edges on the tailcap .(it's the best grey ) the blue grey is the one they give away for like 8$ during super sales (it's the ugliest ) and the only other grey i Know is the older s2 .
Was gonna say “anywhere”, but in Greece? Dunno. Can be had from Amazon (goggle “20mm collimating lens”), and here in the States is LEDSupply, among others. Just got a few from AX a while ago.
So, yeah, kinda anywhere, especially if you find ’em on AX (various suppliers, of course).
Try variants of “20mm”, “lens”, “TIR”, etc.
Here’re those I got on AX, ’though those are 17mm:
Like I said, just goggle around.
Thanks Lightbringer 
Yeah Ive looked on BangGood, they do ship to Serbia surprisingly. Im gonna check that out as soon as I get my card from bank , experts f`ed something up again, been waiting for it over 10 days , hope i get it before the sale ends 
Just to make sure I understand, “just drop” means disassembling the head from the inside, correct?
Had this drop into my lap today:
So you can get a complete set in one shot.
Yeh. The whole pill unscrews as a unit, you pop out the reflector and pop in the TIR. Done.
Just make sure the O-ring doesn’t pop out as well, or if it does, reseat it against the inside of the head, then drop in the TIR. Keep it face-down and slowly screw in the pill most of the way, gennnnntly. Lightly tap upwards on the TIR ’til you have maybe 1mm of “give”, then flip it face-up, make sure the TIR is centered on the LED, then snug it up from underneath, also gennnnnnnnntly.
Done.
Also, TIRs made me love the 4C tint (yeah, even above the BBL). I could imagine what a 4D would be. 
Before it was a urine-yellow hotspot and cold white spill, the definition of a fried-egg beam.
After, with the TIR nicely blending all the light, it’s a beautiful warm-sunlight tint all over.
These are listed as 21.2 mm diameter. That is good for S2+?
I am about to get a couple of S2+ just to play with these (I didn’t have any interest to S2+ until I read about the extra lenses). Do you know if these lenses match with BLF A6? I prefer to get a couple more A6s if they match.
No idea about the A6, as I don’t have one.
20mms have a little bit of “slop” in a S2+, so 21mm or so should still fit. Worst case just sand a bit around the edges.
Lightbringer, why don't you own an A6? Just cureous. Thanks!