here are cheap spokes on Amazon but I’ve read that they have issues, like not being quite the correct length or the nipples stripping too easily.
Stay away from the cheap spokes on Amazon. I have probably built 8 wheels with them. Got burnt twice. There are two brands on Amazon. One sent me spokes that weren’t all the same length and the other came with nipples that stripped when tightening. Not worth the risk.
I have had decent luck with Porkchop BMX cut to length. Also husky bicycles has some good deals , but you have to buy the whole box.
Just take your time with an online spoke calculator. They work fine as long as you get your measurements right. Happy to help if you get stuck.