Hi. I’m looking for some 18650’s to put in a 20+ cell pack to power a project I have in mind. Budget is $150 USD, though I’d prefer a lower figure as long as I’m not drastically compromising on safety. Cell protection is not needed, and the cells will not be in an air-tight enclosure. I’m not looking for high-discharge or high-capacity cells, just something that’s relatively cheap but reliable. A capacity as low as 1600mAh-2000mAh per cell is acceptable. Thanks in advance for your suggestions.
A twenty cell pack isn’t something you just cobble together.
You need sophisticated balanced charging circuitry and quality matched cells.
check out ali express. You can get good quality batteries with tabs.
Sanyo 2600. Try Keeppower, $3.50 per cell + $0.85 shipping per batter for 100, you should be able to get 50 in at less then $150. Panasonic 2900 are $4.30 per cell per 100 + S/H
Although as others have said above: Safety, safety, safety.
20+ li-ions! What on earth are you building? First off I wouldn’t even think about building a multicell pack without at least some way of balance charging it, let alone a suitable protection circuit (which might be difficult given the possible size). Second, buy quality cells from the same batch from a reputable seller and test them all for charge cut off and self discharge using a decent charger and DMM. Third, buy cells with tabs, if you can - soldering direct to cells for that big a pack won’t be any fun at all. Fourth, show us pics when you’re done!
I didn’t mean to come across as a naysayer, I just think something like this needs a lot of thought and care going into it to be safe. That many li-ions will contain a considerable amount of energy and cost a lot of money, so getting the design right first would be a good idea.
Hi again. I wasn’t expecting so many replies in such a short time! I do appreciate all your concerns about the safety of the pack.
(1) Good point! I’ll look for protected cells from now on and, if needed, will stretch the budget a bit to allow for them.
(2)The cells will likely be soldered in a 4s5p configuration and will be charged with a hobby charger with external balancer.
(3) Budget does not include chargers or holders.
most of the people I know that make large packs protect the cells at the pack level, in your case using a 4S PCB which are quite readily available for ~$15 or so. I’m not entirely sure why, cost perhaps or possibly because you don’t want individual cells dropping out and screwing the rest of the pack. Another thing to consider is that pack PCBs are usually more conservative about the low voltage cut off and better at enacting it than the majority of PCBs that are sold on individual cells. One more thing too - you won’t find protected cells with tabs 
what’s the pack for? You won’t save a huge amount by going with lower capacity cells, but higher capacity cells will drastically cut the weight of the pack and the amount of soldering you’ll have to do. A 4S5P pack with 2Ah cells will contain about the same energy as a 4S3P pack with 3.1Ah cells, cost ~$20 more and weigh ~400g less.
Why not buy LiPo packs?