I need to replace a wall unit a/c, since they are much more expensive I was wondering if I could use a window unit instead?

Yes you can use a window unit if it will fit your window. Measure your window before shopping.

Thanks for the reply, however, the a/c will not be going in a window. I am replacing one in a wall with a cage. Do all have the intake in the back?

Then you better check for the intake and exhaust for the condenser (outside) heat transfer area. That is one item that makes the wall a/c unit different from the window unit.