My Kombini, a japanese e-tailer, has Gotenks for about $72.00 CAD with free shipping on Ebay. They are a trusted seller (I've purchased from them many times and no issues). Here's the link:
https://www.ebay.ca/itm/S-H-SH-Figua...MAAOSws29b1qlC
Goku Black is definitely going to be hard to find at an affordable price. Maybe check EB Games, they might have him for preorder.