Slant to open? That could mean a lot of different things.
If you can determine where it's leaking, a tube of caulk might work as a temporary fix as long as you can redirect the water to allow it to cure. If it's direct rain falling on it, you may be better off getting some duct tape and plastic....or a small piece of trim and plastic to make a tent over the opening. That may be a better temporary fix until the weather dries up.
You can find cheap windows if you look around. Basement type windows can often be utility grade if the space isn't well insulated to start with. Just consider that when specifying what you're looking for and you may save a lot of money. Replacement windows can be ordered the exact size of the opening and you simply shim and caulk around them to create a seal.
Additionally, you can get rolls of window flashing that allow you to seal the outside of window to the side of the structure. It sticks on and uses a tar substance to form a seal with an outer foil membrane. A more permanent temporary fix, would be finding some aluminum flashing and possibly making a small awning over the window to direct water around the window opening. Without seeing pictures and knowing what kind of water you're dealing with, it's tough to say what's overkill and what's not. I'd definitely get a quote on some windows for the ones that need to be replaced or find someone that may be able to fix them. You may not need to replace them all and who knows if they can be salvaged. Sometimes, they can be reworked and resealed if the metal isn't too far gone.