It might be a decent razor. It might only be a decent practice razor. It's going to depend on how deep the rust is on the edge on the toe end. If it's just surface rust, it might hone up just fine and you will have yourself a perfectly serviceable razor. On the other hand, the rust may be deeper into the edge and it will take a heck of a lot of metal removal to get to the good stuff. If that is the case, then you will have ample opportunity to gain some honing muscle memory!

You did just fine with your purchase, UNLESS you thought you could buy a $10 razor and just start shaving. Given that you are on this forum, you probably already know that is not the case. If you want a razor to practice with, you can't go wrong with a $10 razor. Now if you want a razor to shave with, you are going to have to invest more time and money. Good luck with it!