I think it would depend on what is available in Colombia or whether or not Colombia has import restrictions on ordering them from overseas. Do you know of any in-country suppliers of Molicel P42A cells? Can you order cells from other countries? Can LIPO packs be ordered in-country (in Colombia)? The thing about making your own packs is the cost associated with getting started, and the danger associated with learning how to do it safely. A spot welder is at least 450,000.00 Colombian Peso.
There’s also the problem of sourcing the nickel stripping, which usually has to be ordered from China- Aliexpress. One must also find silicone wire for series connections, leaded solder, and heat shrink insulation.
The LISHEN 21700 4000MAH 35A BATTERY (LR2170LA) is the cheapest 21700 I know of that can be used for esk8 but it’s not much cheaper than the SAMSUNG 40T 21700 4000MAH 30A BATTERY, which it is attempting to copy. The Samsung battery is what I would go with. Molicel P42A cells are currently sold out, and they cost more.
Does Juan have a battery compartment? What kind is it? 4 of the Zippy cells could be purchased here for roughly $212 USD. That’s probably his cheapest option though I don’t know what shipping would cost from The States.
Lipos are a pretty bad choice for electric skateboards, they tend to drift and balancing then is always a pain in the ass, replacing them often will be more expensive than switching to a Li-Ion battery pack.
I understand that if the budget is low do not try to use cheaper cells, use a cheaper battery pack will less cell count such a 12s4p or 10s4p, but try to stick with P42A cells, if cost is still prohibitive get 18650 30Qs.
But my advice would be to not get cheap with batteries, select the range your friend would like and design the battery accordingly 12s6p or 12s8p is a popular choice these days, the reward, practicality and joy these machines give you outweights by far a one time battery cost.