Is the inside of the handle plastic or metal? Either way if you can clean it up and rough it up, and same with the tang, maybe even use a file, metal epoxy will hold it as good as anything, short of actually welding it, or extending the tang with a weld. You don't need brand name metal epoxy, I have seen stuff from china that looks pretty good. Epoxy resin with metal in it. It holds really well and is easy to work with and file or sand with basic tools.
I know the price of things everywhere have gotten crazy, and I don't know your budget, or even what the sword market is like where you live, but over here you can get a real forged carbon steel blade from China without spending crazy money. Even at the bottom end of the market you should be able to get a sturdy and reliable blade. Just make sure it has a full tang. Higher quality fittings, real rayskin and leather wrap for the Tsuka etc can push the price up. As can clay tempering with a real hamon line. A lot of the extra features are unnecessary for a straightforward practice blade. Unless you are going crazy with cutting tatami mats or other heavy use you should be fine.