breeder overseas use like half that size. however they do constant water changes and many commercial breeders use growth hormones in the food, which is a really crappy practice. using the growth hormones a betta that could with excellent care live to 4-5 may live 1-2 years. stress shipping and small homes all shorten a bettas life span. a home breed betta from good stock, never stressed and always in good condition can live a loooonnnggg time. one of my friends bettas is 6+ at this point.
anyways the bigger the jar the better, you can use canning jars but bettas give off a sort of anti growth hormone, to make its siblings smaller and cut out competition. to get your babies to grow healthy very frequent water changes are crucial.
what I also used was whatever jugs/jars I could find, glass was best, but if I had a huge spawn I didnt hesitate to use really well cleaned one gallon water jugs. Id cut the top in a circle, leaving about and inch before I cut it totally off to act as a hinge like lid. I got good at judging size and health from looking down and the opaque plastic also cut down on the stress of the boys seeing each other constantly and flairing constantly.
also big question, how do you plan on heating the jars? unless you live in a very warm climate they need to be kept warm some how or else can get stressed and die or else the cool water will make them grow extremely slow and can even stunt their growth. what i did was for a small spawn was use a large reptile heat mat under the jars, you need to set everything up and check the temp in the jars for a few days, you may have to use a mat or two between the jar and the heat mat, but with a little patience you can get a very even temp this way. if you end up with a huge spawn the easiest way is to heat a closet or a very small room, like a spare bathroom with the safest heater you can find. an oil filled radiator type heater is what I used because even in the closet (mine was large and not cramped) it wont catch fire if something falls on it, it has many temp and time settings and mine is adjustable to go on and off to keep an area a certain temp.
go ahead and post in the wanted section, thats how quite literally I got all my betta stuff. I really do wish you lived closer. my sister and I no longer breed and have been trying to get rid of everything.