Lolly sticks. Got a bag of 1000 a couple of years back for another project....perfect for almost everything.
I had to work with lolly sticks to build my
repeating crossbow, but sometimes using balsa is much quicker and leads to better results.
Lolly sticks have all the same whidth, which is really practical, but they have to be cut on both ends, and cutting that wood is much harder than working with balsa... that's more expensive, but with 5$ you're probably going to have enough for the whole building plus something!

Cheers
Jack